1992 Other Oldsmobile Models radiator cracked

As I pulled off the highway yesterday my engine was overheated, steam coming from under the hood. I pulled over and let it cool down, went to a filling station and filled the radiator with water. A lot of it. Couldn't see anything in the dark, so I went home (just down the street) and today when I looked, there was a crack in the radiator, near the top, opposite side from where the radiator cap is. I know that metal radiators can be repaired, but I think this one is either fiberglass or plastic. Is there any way to repair it, or will I have to buy a new one? I'm pretty broke, so I don't know what I'll do if that's the case. Reading around some on the internet, I also wonder if there is something else wrong with the engine that made the radiator crack. Does this just happen to old radiators or must there be something else wrong? Please help!