Is there a problem with my headgasket? ( 1992 tbird 3.6 L en

My friend was driving my car and let it overheat. I hadn't driven it for awhile and before starting it I had a mechanic check it out and he said that everything was fine.
While my friend was driving it he said he noticed the temperature was way hotter than it was supposed to be. Then the check engine light came on. I couldn't see any of this from where I was sitting in the car ((he mentioned it long after it happened and we had already pulled over)
I noticed this weird smell like melting plastic, then steam came out from under the hood and I made him pull over. My overflow tank had melted.
Anyways I opened the radiator cap and noticed it was all oily where water is supposed to be. There was also white smoke coming out of the exhaust. ( I thought because I hadn't started it in a long time)
People have told me it was the head gasket that caused the problem. A mechanic quoted the price of getting it fixed at over 3, 000 dollars which I can't afford. ( I'm 21 years old and work retail) to be honest I wasn't sure if he was telling the truth about what he thought the problem was or just wanted to make some money)
My friend said he would get a family friend who knows a lot about cars to fix it. ( The family friend is not a mechanic)

I was just wondering if this seems like it is in fact a headgasket problem and if it would be a really BAD idea to let someone take apart my engine like that in a home garage.
Any advice appreciated