What if it wasn't your plane? Would you know that about all of them?
What if it wasn't in your hangar? Would you go get it or try to fix it on the ramp?
What about another dozen or so things that might be reasonably expected to require time to accomplish? Any paperwork? Any parts research necessary? Any M/M research necessary? Any cleaning, tightening, rigging, testing, connectors, grounds, other stuff to be wrung out and checked? Any time required to troubleshoot and be sure it's the alternator vs regulator, wiring, or other electrical issues?
Engine runs necessary to validate or test? How many? How many techs required? If it's an intermittent problem, do they keep working until they find it or throw up their hands and quit?
Anybody who's BTDT knows all these things are to be expected from time to time, but nobody (AFAICT) knows exactly when/why/how they will manifest themselves. Some of them drive the shops crazy, including the good ones.
Not saying any, some or all of this stuff came into play on the job that's been mentioned, the bill could be nothing more than a blatant screwing.
But it's also nonsense to believe the "well I coulda done it in X" from people who have absolutely no clue about the facts surrounding the job.