The process part
Print, place, reflow, inspect and test. It scales with placement count, pitch and the number of assembly passes.
The DIP part
Through-hole insertion plus selective or wave solder. Labour content depends on lead count and whether parts are hand-inserted.
The material part
The BOM at quoted quantities, with manufacturer and lead time stated. This is where most of the difference between quotes appears, so it deserves the closest reading. Read the three parts separately and the pcb assembly services quotations become comparable line by line.
