1. There have been a couple guys that have tried to service them, but I think in the end they changed the head.
2. I have seen them from $3-500
3. I have seen them in the classifieds from time to time for $150-250
4,I would leave things alone until the truck is running normally, Then decide if you need to then. A new head can revive a somewhat tired engine.
I would buy a new or factory reconditioned head not a used one, unless it has a warranty. It will take you about 3-4 hrs to change, You don't want to do it twice.
Before you pull the head , did you check the fuel cut off rod behind the cover with the two screws where the engine shut off cable goes?