Box build assembly cost is set by more than the parts on the bill of materials. The unit price on a quote is the visible tip of a stack that includes materials, assembly labor and complexity, how volume and one-time engineering costs are amortized, the depth of test and inspection, traceability and regulatory work, and where the work is sourced. Two quotes for the same product can differ mostly because they drew those lines differently — so compare them on total landed cost and scope, not on unit price alone.

This guide breaks down each driver so an OEM team can read a quote, see what a supplier included or excluded, and ask the questions that make competing prices comparable.

The main cost drivers

  • BOM and materials. The dominant line for most box builds. Cost moves with component selection, specialty or single-source parts, distributor availability, and how much of the material the supplier procures under a turnkey scope versus what you consign. A part that is not stocked by standard distributors adds both cost and lead-time risk.
  • Assembly labor and complexity. Connector count, cable dressing and routing, mechanical fastening, torque and bonding steps, and how accessible the assembly is all change the labor content. A dense enclosure with hand-routed cables costs more per unit to build than a simple bolt-together.
  • Volume and NRE amortization. One-time engineering, fixtures, test development, and setup are spread across the run. At low volume those non-recurring costs weigh heavily on each unit; at higher volume they fade and material and labor dominate. This is why the same product prices very differently at 100 units and at 5,000.
  • Test and inspection depth. Functional test, in-circuit checks, environmental stress screening or burn-in, and inspection each add equipment, time, and documentation. More test buys more confidence and costs more — the right amount is set by the product’s risk, not by a default.
  • Traceability and regulatory work. Serialization, records, controlled processes, and regulated-industry requirements add real, recurring effort that belongs in the price.
  • Packaging and logistics. Custom packaging, kitting, freight, duties, and delivery to multiple destinations are part of the landed cost even though they sit outside the assembly line.

Offshore vs local: how sourcing changes the math

Where the work is done changes several drivers at once. Offshore assembly usually wins on unit labor cost and can hold deep component sourcing, but adds freight, duties, and longer lead times, and puts more weight on clear documentation because the feedback loop is slower. Local assembly can shorten lead time and simplify communication at a higher unit cost. The right answer depends on volume, how time-sensitive the program is, and whether the BOM has parts that are easier to source in one region than another.

Representative project (anonymized). An IoT-device customer was bringing two new controller boards to production — a four-layer main controller and a two-layer sense board — and wanted to compare offshore assembly against a local assembler on both cost and lead time before committing to 500 units of each. Two things complicated the comparison: the BOM included a specialty BLE module that standard distributors did not stock, and one part was customer-supplied and had to be kept out of the turnkey quote. The response was a granular, per-stage quote that separated the turnkey-sourced material from the customer-supplied part and broke out lead time by stage, so the customer could compare like-for-like against the local option rather than a single blended number. The lesson generalizes: a comparison is only fair when both quotes name the same scope, the same excluded parts, and the same test.

Compare total landed cost, not unit price

The cheapest unit price is not the cheapest program if it leaves costs off the page. When you compare quotes, add back everything the unit price may exclude: non-recurring engineering and fixtures, freight and duties, test development, customer-supplied parts that one quote assumed and another did not, and any rework or expedite risk implied by a thin plan. A slightly higher unit price with a complete, well-governed scope often beats a lower one that quietly pushes those costs onto you later.

How to get comparable quotes

The way to make prices comparable is to send every supplier the same, complete package: released BOM and drawings, the configuration range, the demand pattern, the test intent, traceability needs, sourcing boundary (what is turnkey versus consigned), and delivery destinations. See how to prepare a box build RFQ package for exactly what to include, and how to choose a box build assembly manufacturer for reading the responses. If offshore sourcing is on the table, box build assembly in China covers how that option is scoped and governed.

Priced this way — on a shared scope and total landed cost — a box build quote becomes a decision you can defend, not a number you have to trust.