1997 Pontiac Grand Prix Head Gasket

I'm looking at possibly purchasing this car for my wife. I'm told by the previous owner who just bought it for his 16 y.O. Boy who is not interested in the car, that a diagnostics was done on the car before they bought it and the only thing that came up was the head gaskets were going to need replaced. I test drove the car and when I got back and parked I could smell oil. I looked under the hood and noticed oil on the passenger side in the engine compartment. I only drove it appox. 2 miles and I did get on the acceleration to see what it would do. My question is how much do you think a repair job would run and is this something I could possibly do on my own with help from a friend? I have some knowledge of repairing cars and have a friend who could help and he has more knowledge than I on repairs. The only problem is we both have bad backs. Also is there anything else I should look at other than the obvious of making sure the heads are not cracked?