Good with cars? Help me out, compensation provided

I own a used car with a bad transmission. Two mechanics told me my car can die at any time. My best bet is to either get it rebuilt, or change it out with a new/used transmission. I think my cheapest option is to buy a used transmission myself, and put it in myself. However, I don't have the background knowledge to do this. If you think you can help me out, please let me know. I will provide compensation, and we can discuss how much.

Thanks!