There are 3 prices for parts you but from a parts store: Wholesale, retail and list. Wholesale is what your mechanic pays, retail is what you’d pay if you bought it at the same store, and list, the highest, is what you pay the mechanic.
It’s always been this way, it’s the same with everything you buy. Every time someone touches an item they mark up the price. If you don’t want to pay list price, buy it and install it yourself. This is how capitalism works.