He also used flux, 95% silver solder, emery cloth, some rags, gas in the torch, etc. None of that sruff is free. Most companies in ANY trade have to build in a charge for such materials in some way. Your auto mechanic probably adds a small line item for "shop materials" etc.
Copper pipe is sold by the 10' piece, not by the foot. Luckily he probably had a few pieces of scrap laying around so did not have to charge you for the whole 10'; but those ells are not free either,