I have a simple rule when pricing up boards for volume manufacture:
I ignore the cost of generic, small passive components completely.
It's not clear from your post whether you're planning to build these boards by hand yourself, or whether you'll be contracting out manufacturing, but either way it's never going to be worth the time trying to get the best price for grit.
If, say, an 0603 resistor costs £0.145, more than likely it just means the supplier wants to make £0.141 on each one, probably because it's an odd value. You're paying for snipping a few bits off the reel and sticking them in a labelled bag, not the parts themselves.
When you get to volume manufacture, where the cost may actually matter, you'll be buying parts by the reel anyway, and the price will be completely different. More than likely, it'll be vanishingly insignificant compared to the active components, board, enclosure, assembly, testing, approvals, packaging, shipping, and any other overheads you can think of.