Depends what was done and what needed done.
Not uncommon to just need seized front mech “adjusted” as it’s not shifting right.
Actually requires new mech, chain, chainrings, cassette and cables and outers.
Add that up + labour (internal fidly) cables and the service could be a bargain.
Obviously I’m not saying this is the case in this example but I bet there is more to it than made out. No offence meant to the op but perhaps you are only hearing half of one side of the story?
Clearly the shop should have called the customer to advise of the extra costs involved.