FWIW! We get a lot of bent RD hangers at our shop. I usually charge only $10 to align them. It's quick with the Park tool and experience. The Park tool is worth it. I'm convinced that people don't pay attention when they lay the bike down, or when they hang it on a rack or put it in the car. RDs get banged all the time so the hangers get bent. I align them so they show less than 1/4" out at the rim, both directions. On my own bikes I align the hangers closer than that, after aligning the dropouts. It makes a difference in how the RD shifts, especially with indexed systems.
$75 to align the RD hanger? Either robbery or they are doing a LOT more than you've asked for. Ask many more questions!