1991 Pontiac Grand Prix Problems

Well I purchased a Canadian-made 1991 Pontiac Grand Prix with about 181,000 miles on it, but in Canada, their system is ran by kilometers, so this means that this car has about 90,000 miles in the Mile system. Anyways. About 2 weeks ago I was driving home from Phoenix and my thermostat kept flucuating from normal to really hott and then it finally stayed at hot, so I pulled over and sat for a while and then drove to the nearest Shop and I replaced my water-pump because that was the problem at the time. Well, my thermostat stayed stuck on above hot and the mechanic told me that I needed to reset my gauges and then it should go back to normal, I never did that, but it stayed like that and ran fine for about 2 weeks and at the same time this was happening, my windshield had been fogging up with steam from the engine and continued to do so after I replaced the water pump. It only did it ever so often. So I did not think that there was nothing wrong until yesterday afternoon when I noticed that there was smoke coming from the engine and I checked it and it was fine, but then that night I went to Phoenix and my car all of a sudden had no power and the check engine light came on, so I pulled over and all of a suuden at the light, my car died. I got it to start and drove to a store and it was overheating pretty bad, so I called for a ride. The next day I drove home and it made it barely to the shop and as I turned in my engine shut off on me again. They took it in and did a check and they said that I need to replace one of my head gaskets, raditor-tank(it split), spark plugs, and fluids. They did not know that it was Canadian made, so they thought that it had a lot of miles on it and that the engine probably cracked and that I could not even start it. But I went and started it and it started, the only thing is that it sounds like a gasket is blown, but I dont know what to do or believe? I feel like they are trying to get me to spend money that I do not have, plus could my thermostat cause all this commotion in the engine because it was not working properly? What could cause this? Please help me so that I can get my car fixed.I need a second opinion!

Denessa :( [/b]