Hello Red,
Sorry for the bad news. I would first try re-torquing the head while engine is warm. Loosen the radiator cap before beginning to relieve pressure. Loosen a head bolt one full turn then re-torque to specs (I would take it up to 70 ft. lbs instead of the lower specs. under these circumstances). Do this one head bolt at a time in reverse tightening sequence.
Adding sealers to the coolant is normally not a good idea. The sealer will travel to all parts of the cooling system and may clog up other things.
Cost depends on the labor rates and experience of your mechanic. The big problem is figuring where to stop. You may have to decide on whether to re-condition the head or possibly more before replacing the head gasket. At the very least consider replacing the timing chain if it has close to 100,000 miles on it. Good luck, keep us up to date.
Joe Alexander
Blacklick, Ohio
