[fuzzypuppy]

You don't have to replace the complete engine for a bad valve.
just pull the heads and have the heads reworked, if you really have a tight budget just pull the offending head and have only the one repaired.
Vortec heads new from the dealer are not even all that expensive.
last I checked they were about $ 500.00 a pair brand new.
I had a pair of vortec heads in the machine shop 4 years ago to get refreshed and I believe they charged me $ 125.00, I pulled and installed the heads myself, so if you have someone else do the labor you'll have to add labor cost as well.
hope this helps. good luck