If the detailer is performing 2 step correction (compound and polish) then the price is ok. But for one step correction, price is bit high.
I would prefer not to go for 2 step correction for such an old car. Also remember, paint correction will not repair cracks, it will fix faded color, scratches, etc.
A good detailer will always take a responsibility of educating customers what could be fixed and what couldn't.