Let me add few more lines on this topic:
If you just need couple pieces of the chips (for the satellites, missiles, ...) fixed cost might be your major concerns. Tools (simulator, synthesior, backend, ....) Engineering, testing tooling, masking, will take a lion share from your expenses.
If you want to deliver 100 M pieces of your design (DVD decoder for example), floating cost will take the major parts. Manufacture cost: testing pattern cycle, tester type, wafer price, packaging type,.... will be your concerns...
Cost is important.... but schedule might be one other major issue too