A quote for a machined prototype often lands with a wide price band: two suppliers give you the same drawing and the gap between their numbers is a factor of two. Before you push for a lower unit rate, work out what the price actually contains. A useful comparison for product R&D acceleration and low-volume work covers four lines — what has to be made, how it will be inspected, how many times the design may still move, and what happens after the first batch arrives.
Start with the print, not the price
Prototype cost is driven by tolerance and inspection far more than by part size. A bracket held to ±0.1 mm can be cut and reported with hand instruments. The same bracket at ±0.01 mm usually means slower machining, a controlled measuring environment, and a dimensional report for every piece. Ask each supplier to state, in writing, which features they treat as critical, how those features will be measured, and whether the measurement result travels with the shipment. If one quote includes a CMM report and the other does not, you are not comparing the same product.
Material availability is the second quiet cost. A specification that names a single grade from one mill can leave a buyer waiting on a mill lead time, or paying a cut price for a small quantity from a distributor. Where the function allows substitution, say so in the enquiry and ask for alternatives with their trade-off spelled out — stiffness, corrosion resistance, weldability, polishability. A substitution that a supplier proposes early is cheaper than the one a purchasing engineer discovers late.
Count the inspections and the rework you expect
Prototype quantities are small, so one scrapped batch hurts more than a slow cycle. Compare quotes on their rework terms: what a supplier will remake at their cost, what they consider a customer-side change, and how fast a remake can be started. A slightly higher price that includes a remake allowance is often cheaper than a low price plus a paid second attempt.
Testing belongs in the same budget line. Functional prototypes need hardware testing: fit checks, thermal or load cycling, sealing and leak tests, or a run on the assembly line the part is meant to serve. Some shops quote machining only, and leave you to find a lab and a fixture. Where the supplier can build a simple test fixture and run the check themselves, ask for the cost of the fixture and whether it stays available for later batches. Fixture money spent once and reused across revisions is far better value than paying for a new jig on every round.
Budget for design changes, because there will be one
Most prototype programmes carry at least one revision after the first parts are in hand. Price the work in rounds rather than as a single lump sum, and ask what a change costs at each stage. A drawing change before cutting is nearly free. The same change after a fixture has been made and parts have been cut means new setup, new inspection data, and a new lead time. A supplier who supports product development alongside manufacturing will normally flag which design choices raise cost before the file is released, which is where the saving is largest.
Write the revision plan into the purchase order: number of rounds included, cut-off dates for each round, and who owns the tooling files and inspection data between rounds. Keeping those files on your side keeps a second supplier able to quote the same part, which keeps your negotiating position intact when volumes rise.
Price the step from prototype to production
The prototype order is rarely the end of the spend. Ask what changes when you order one hundred or one thousand pieces: which process the supplier would switch to, what new tooling that requires, and what the new lead time looks like. Also ask whether the same shop will make the production parts, or whether they expect a different supplier to take over. A handover is manageable when the first supplier documents their setup, and expensive when they do not.
If the end product also needs cleaning, coating, bonding, or an assembly station around the prototype, that equipment belongs in the same plan. A vendor running manufacturing automation and custom equipment work can tell you early whether a design will need a dedicated fixture or station in series, and roughly what that adds. Finding this out during the prototype round costs an engineering conversation; finding it out after tooling is ordered costs a re-quote.
A short comparison sheet to run before you sign
- Same drawing revision, same quantity, same tolerance callouts on every quote — otherwise you are comparing different scopes.
- Inspection method and report format written down, including who pays for the measurement time.
- Rework terms and lead time for a remake, stated before you need one.
- Test fixtures and testing scope priced separately, and marked as reusable or one-off.
- Cost of each design round and the cut-off date for changes.
- Tooling and data ownership, so a second source can quote the same part later.
- A production estimate with tooling and lead time, so the scale-up step is not a surprise.
Two suppliers with similar rates can still give you very different landed cost once inspection, rework, and revision rounds are added. Build the comparison sheet, send one clean package of data, and read the answers side by side. That is usually where the real budget decision gets made.
