I totally stripped the threads on my crankarm once. The shop where I bought it is a pretty good shop. They installed a HELICOIL into the crankarm. Charged me about $20. Much cheaper than a new crankset. Been about 11,000 miles on the bike with no problems.
Just a note: I did take it to another shop first. Ithought they were a pretty knowlegeable handy shop (shop A). They suggested shop B so some shops may not be equipped to do the repair.