Thread repair inserts are your cheapest solution and might do the job, but are dependent on the skill of the installer, and the condition of the plug hole.

My son's '81 arrived into our household with 265k mi and an insert in the No.2 hole. This had been installed by an indy Volvo specialist. It blew out on an on-ramp to the 101 freeway during rush hour in Santa Barbara. Home it came (35mi) on a flat deck.

I took the head to a specialist cyl. head rebuilder, They welded and rethreaded the bad hole, skimmed the head .010", gave it a valve job, all new seals and hushers, and returned it looking like new. Even the valve clearances were right. $250 (in 2002).

In reality, it's probably more economical to get another head from the yard (with a guarantee) if the thread insert fails to solve the problem.
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Bob (son's 81-244GL B21F/M46, dtr's 83-244DL B23F/M46, my 94-944 B230FD and 89 745 (LT-1 V8); hobbycar 77 MGB, and a few old motorcycles)