One of the guys here that fixes amps as a living will be able to tell you for sure but....
Unless you have to pull/lift the eyelet/turret/PCB board to get at 1 of the cap cans and even then that's seems like a lot of money to me. And like you said the guy didn't even address the hum issue which you did easily. Our host Doug charges $16.50 for a F/T 50uF/50uF/500v cap. So that $49.50 + say ~$5 shipping would be $54.50, + a buck or 2 for the bias cap. So $225 - $56.50 = $168.50 for an hour or so of work?
the "tech" put one of those stickers "for servicing call--" right on the back of a vintage Marshall that was flawless!
That was probable common back in the 60's/70's but.... I wouldn't be too happy about it now.
To me 3 things stand out as red flags here;
1. Didn't address what was asked to be fixed?
2. Over charged?
3. Took the liberty to share his service sticker for return business because his work is soooo good?
To me add them up and I get the felling he thinks a little to much of himself and he thinks knows better than the customer to bother to listen and since he's so much smarter than the customer and his work is soooo good he deserves the big $$'s?
Yeah right.

I think you just got yourself a new customer my friend and you deserve it. You listened and fixed his amps problem.

Keep it up, you'll get more by being honest and actually fixing what needs to be fixed and not what you think needs to be fixed, 2 different things sometimes. But people with big egos can't or won't see it.
Brad