Unless your customers are price-shopping you (which means you probably don't make money on them anyway), you just add your desired margin to your cost and that's the sale price to the client. We add a flat margin to every computer we sell (it's graded, $X for <$1000, $Y for >$1000, < 1500, and $Z for >$1,500). We don't put model or part numbers in the quote, we just list the specs & show the final price. We get very little pushback and that guarantees our margin. Same for residential.