1999 Ford Contour Heater Resister or something else?

Heater problem
1999 Ford Contour Automatic 104000 miles

When I have my heater blower on, panel blower or even defrost, after the car warms up I smell what seems like exhaust fumes. Midas THINKS it may be the heater resister because I only have one speed working, the highest speed and the wires on the resister may be burning out. They also think the smell is a burning smell, I say it does not smell like anything is burning. The problem is, I can't afford to have the heater resister fixed and then find out the problem is something else. Can you tell me what the real problem could be? Thank you. LMC226