Have you already tried negotiating with RISD? It's absolutely worth a shot to let them know that you got a better offer elsewhere and are on the fence, and to ask if they can give you more competitive funding.
If that doesn't work, I agree with the previous comments. Unless you are significantly more excited about the faculty at RISD, I would vote for UW Madison. I strongly feel that it's not worth going into that level of debt just for the name on your CV. What's much more important is the work you come out of the program with, and it sounds like Madison is a better fit for you and would give you better support for focusing on your work.