I've been reading a link about the average labour rate in the US,
It seems the rates are fairly comparable to the UK labour rates, for $250 i'd expect it done in a proper workshop, albeit an independent, based on $75 an hour and allowing an extra hour above the three quoted for 'any little issues'.
Someone working from home on their driveway with the help of their family, i'd personally offer around $125, if I could get away with $100 I would, my logic being $25 an hour for a diy'er and giving an extra one or two hours above the quoted repair time is quite fair, for a diy'er, for which you wouldn't expect to pay top trained technician rates to.
A good technician on a slightly higher rate may well get the job done quicker and more competently, for which you would expect to pay higher than a diy'er.
I know garages that would work for the $25 an hour, with their overheads factored in!
Maybe get a few more quotes.
If there is anything else I can do to help, please do let me know, if this helps you please rate 5 stars ;)
Good luck, I hope you get it all sorted soon.