Who is doing the repairs. Some shops will charge a small fortune per service hour, but if you can do it yourself or know someone who will help you, you can save quite a bit.
What is wrong with the amp? Fried output transistor? Probably worth the time and trouble to repair IF you can find someone who will work with you.
What is the replacement price of the amp? If you can get a new one for cheap, don't bother with the repairs.
Sorry that I can't be more specific, but that's the best anyone can offer.