I just got done fixing head gasket on my pontiac gt 02 v6, It will cost you 800+$ to have someone else do it, I was lucky enough to personally know a diesel mechanic who helped me fix it.
Ended up being a seal that got warped, coolant/oil got mixed in with the gas, white smoke, smelt horrible, and sounds horrible.
Lucky I didn't warp any heads either.
To replace all the seals, and bolts it cost me about 250$, but you have to tear down the engine to its core.
Runs better than before, and I'll probably sell it soon, as I enjoy my 92' jeep cherokee with the most reliable engine I6