VAPI vs Retell vs Pre-Built: What Contractors Should Actually Choose

You have been pitched a custom AI voice agent built on VAPI or Retell by a dev shop for $5,000 to $15,000 upfront plus $0.15/minute ongoing. The pitch sounds compelling. It is almost always a bad deal.

VAPI and Retell are infrastructure platforms. They are to AI voice agents what AWS is to web apps: powerful primitives that require real engineering to turn into a working product.

For a $1M to $10M contractor, the math does not work. Here is why, and what to buy instead. For the buyer's-guide pillar, see our AI voice agents for HVAC 2026 guide.

What VAPI and Retell Actually Are

Both are developer platforms for building AI voice agents. You get APIs, SDKs, and a web console. You are responsible for writing the prompt logic, building the CRM integrations, handling telephony routing, and maintaining the whole system over time.

VAPI (vapi.ai): API-first, developer-focused. You pick your own LLM (OpenAI, Claude, Groq), voice (ElevenLabs, Cartesia, PlayHT), transcription (Deepgram, Whisper), and telephony (Twilio, Telnyx). Maximum flexibility, maximum integration work.

Retell (retellai.com): More opinionated. Drag-and-drop interface with a flat $0.07/minute bundled price. Built to be faster to deploy than VAPI. Still requires engineering to wire into your CRM.

Neither is a finished product for contractors. Both are starting points for a dev team.

The Real Cost of VAPI (Not the Sticker Price)

VAPI advertises $0.05/minute. That is the platform fee. Actual delivered cost includes five other layers.

Per Telnyx's 2026 VAPI pricing breakdown, true delivered cost lands between $0.23 and $0.33 per minute. The stack:

VAPI platform fee: $0.05/min
LLM (GPT-4 or Claude): $0.04 to $0.10/min
Voice (ElevenLabs or Cartesia): $0.06 to $0.12/min
Transcription (Deepgram): $0.02 to $0.04/min
Telephony (Twilio or Telnyx): $0.015 to $0.03/min

Stack that up at the midpoint and you are paying $0.28/minute. A 3,000-minute month (about 450 calls at 6.5 minutes average) lands at $840. A 5,000-minute month hits $1,400.

That is just infrastructure. You have not paid the dev shop yet.

The Real Cost of Retell

Retell bundles the LLM, voice, and transcription into a single flat rate. $0.07/minute plus $2/month per phone number.

A 3,000-minute month on Retell lands at $212 (including a couple of phone numbers). Much cleaner than VAPI.

Retell vs VAPI per retellai.com/blog/retell-vs-vapi positions Retell as the non-technical-friendly option with warm transfers, batch calling, branded caller ID, and PII redaction included, versus VAPI's API-only posture. Retell is the clear winner on pricing and feature bundling for most use cases.

The Dev-Shop Trap

Here is the pitch you will hear from an agency or freelancer:

"We'll build you a custom AI receptionist on VAPI. $10,000 upfront, $2,000/month retainer, plus pass-through minutes at $0.15/min."

At 3,000 minutes/month, that retainer structure runs you:

$10,000 upfront
$2,000/month retainer
$450/month infrastructure (at $0.15/min markup)
Total year-one cost: $39,400

Compare to Sameday Scale at $789/month for 1,000 minutes, or Avoca at a roughly $1,500/month typical spend for a five-truck shop. Total year-one cost for off-the-shelf: $9,500 to $18,000. Our Avoca vs Goodcall vs Sameday for contractors comparison runs the pre-built vendors head-to-head.

The custom build costs 2x to 4x more and ships months later than off-the-shelf. The full real cost of an AI agent for a home service business makes the line items explicit.

When Custom Actually Makes Sense

There are three scenarios where building on VAPI or Retell is the right call.

Scenario 1: You have 50+ locations and internal engineering. A $10M contractor can absorb a $250K/year AI team. A $200M contractor has to.

Scenario 2: You have a workflow nobody has productized. If your shop runs a weird quote-to-close process that no pre-built vendor supports, custom is defensible. Verify this by running demos with Avoca and Sameday first.

Scenario 3: You are building a product of your own. If you run a holding company or are planning to franchise and want portable IP, owning the agent makes sense. The full build path lives in our how to build an AI agent for home services guide.

For the other 95% of contractors, build-your-own on VAPI or Retell is the wrong move.

Feature Comparison Reality

Retell ships features VAPI does not, per the 2026 comparison on Retell's own blog (vendor bias noted, but the feature gaps are verifiable):

Warm transfers (Retell yes, VAPI no)
Batch calling for outbound campaigns (Retell yes, VAPI no)
Branded caller ID (Retell yes, VAPI no)
PII redaction built-in (Retell yes, VAPI no)
Post-call analysis with custom categories (Retell yes, VAPI limited)

VAPI's advantage is flexibility. If you want to swap in a niche voice model or a custom LLM fine-tune, VAPI lets you. Retell locks you to their stack.

For a contractor use case (inbound answering, booking, emergency routing, outbound quote follow-up), Retell's feature set covers everything and costs less.

What Pre-Built Products Give You That You Cannot Buy

This is the part dev shops will not tell you. Pre-built voice products like Avoca and Sameday bring years of trades-specific tuning that you cannot replicate with a VAPI prompt.

Training data. Avoca has processed millions of trades calls. Their agent knows how to handle a "my AC is leaking" call versus a "I need a quote on a new furnace" call because they have pattern data from thousands of customer shops.

Emergency detection. The keyword set, the severity ranking, the on-call handoff protocol. Avoca and Sameday have tuned this against real customer data. Your dev shop will build v1 in a week and v5 in six months.

CRM integrations. Native connectors to ServiceTitan, Housecall Pro, Jobber, Workiz. These are not trivial. Each CRM has quirks around customer records, dispatch logic, and payment integration.

Compliance. TCPA-compliant opt-in flows, call recording disclosures, state-by-state consent rules. Per the FCC's February 2024 ruling, AI voices on outbound calls require prior express written consent with penalties of $500 to $1,500 per violation, per Kixie's 2025 TCPA guide. Pre-built vendors handle this. Your dev shop will not until your first complaint.

The Real Decision Tree

Read this carefully.

If you want AI voice answering and your shop does $1M to $10M in revenue:

First choice: Sameday ($449 to $789/month flat), Avoca (per-minute, trades-tuned)
Second choice: Jobber's native AI receptionist if you are on Jobber, ServiceTitan's native voice agent if you are on ServiceTitan
Do not consider: Custom build on VAPI or Retell

For the same decision framed at the trade level, see AI receptionist for plumbing: build vs buy.

If you want AI voice + email + quote follow-up + morning brief:

First choice: Sully (pre-built for $1M to $10M contractors)
Alternative: Stack Avoca + LeadTruffle + HubSpot + custom dashboard

If you are a $10M+ multi-location shop with internal engineering:

Evaluate Retell for cost efficiency
Consider VAPI only if you have a niche requirement pre-built cannot serve
Never sign a $10K/$2K retainer with a dev shop without getting pre-built quotes first

Contractor Story: The Dev-Shop Refund

A Texas plumber (anonymous per ContractorTalk's private thread culture, paraphrased from aggregate 2025 discussion on r/sweatystartup) signed a $12,000 build with a VAPI dev shop in early 2025. Six months and $24,000 in retainers later, the agent still could not book into ServiceTitan correctly.

They canceled, paid a cancellation fee, and switched to Sameday. Sameday was live in 10 days at a tenth of the monthly cost. The plumber's framing: "I paid $36,000 to learn that I should have bought off the shelf."

This pattern shows up repeatedly in r/hvac and r/plumbing threads. The common mistake: contractors hire a freelancer or agency who promises "custom" as a feature, not a liability.

What Sully Does That Pre-Built Voice Does Not

Even the best pre-built voice vendors (Avoca, Sameday) only answer calls. Your actual front-office work is broader.

The contractor front office in 2026 has roughly six AI-worthy workflows:

Answer missed calls and book jobs (voice agent)
Follow up on unanswered quotes (SMS + email)
Classify incoming email (new lead, existing customer, vendor, spam)
Chat on your company data (pricing, service history, team schedule)
Morning brief to the owner (yesterday's activity, today's priorities)
Commitment tracking (when you say "I will call back Friday," did you?)

Avoca, Sameday, Goodcall, VAPI, and Retell solve workflow #1. Five others are still open.

Sully is built for those five. It plugs into Jobber, Housecall Pro, ServiceTitan, Workiz, GoHighLevel, Gmail, Google Calendar, Slack, QuickBooks, and HubSpot. It ships pre-built AI agents for all six workflows.

OpenAI and Claude are developer kits. VAPI and Retell are per-minute primitives. Avoca and Sameday solve one thing. Sully solves the stack.

The Math Summary

At 3,000 minutes/month (typical five-truck HVAC shop):

Option	Year-One Total
Custom build on VAPI (dev shop retainer)	$36,000 to $48,000
Custom build on Retell (dev shop retainer)	$24,000 to $36,000
Avoca (per-minute trades-tuned)	$12,000 to $24,000
Sameday Scale (flat rate, 1,000 min included)	$9,500 plus overages
Sully (voice + email + quote follow-up + brief)	depends on plan, evaluate

Custom on VAPI is always the most expensive option. Retell-based custom is second. Pre-built is cheapest and ships fastest.

The 6-Question Test Before You Sign Any Dev Shop

Before you commit to a custom build, answer these honestly.

Have you demoed Avoca, Sameday, and Sully and confirmed they cannot do what you need?
Do you have an internal product owner who will manage the dev shop's roadmap?
Can you stomach 3 to 6 months of build time while your current CSR team handles calls?
Do you have $30,000+ to spend in year one?
Is the workflow you need truly unique, or are you just not aware of a pre-built option?
Are you prepared to own the TCPA compliance, call recording retention, and CRM sync long-term?

If you answer no to any of these, buy pre-built.

The Wrap

Build-your-own on VAPI or Retell is a trap for most contractors in 2026. The dev shops selling it are selling their own retainer, not your ROI.

Pre-built voice (Avoca, Sameday) gets you 90% of the value at 25% of the cost. Pre-built end-to-end AI platforms (like Sully) cover the other five workflows that voice alone does not solve.

Spend 10 hours on demos before you spend $30,000 on a custom build. Your bank account will thank you.