uncle daveO one of the biggest things you left out was r&d if you only make 2 of something and spend 100 on design and tooling,then you have 50 in each plus all other costs.if you make 100 of same then r&d is only 1 each,or if after the first two go out 100 more are requested then r&d should be 0 because you made it back on first 2[to bad it seldom works that way]that is one reason prototypes or so expensive,you pay r&d up front[unfortually the manufacturer keeps adding it in on produciton runs in most cases even when it already been paid for]