This has always been a challenge to me
and I tend not to bid firm fixed price on a
development job; there are too many
unknowns (which you would do well to
enumerate, track and ensure that any
contract holds the provision for "change
of scope" should anything not in the work
package arise from customer change-order
or incomplete original requirements, etc.).
When I was an employee my management
would pad out anything I gave them by 2-3X
(cost, and schedule), that's how wrong I
have generally been about effort and
expense.
I note that some things are missing from
your "cost item" category-list. Such as the
need to make a profit, to cover involved
overhead, reviews and program meetings,
and so on.
I might suggest you look at costing the job
on two bases - FFP, and "time & materials".
Development often makes more sense
as the latter (not to say that customers like
it), while production should be the former
as by that point all unknowns other than
customer demand profile should have
been chased out.