helicoil cost

The guy cross threaded the spark plug and blew it out. I have the head off the engine. How much would it cost for a machine shop to helicoil the hole?

Go to Pepboys. You can buy the kit for around $20.00 as I recall. A shop will be a bit more and you may have to wait some time.

Machine shops I have used want between $25 to 50 each, depending on how many plug holes require the work. If you can take a head off you can install a helicoil yourself.