97 Jetta AC blower - only works on high speed
 

I've got a 97 VE Jetta GLS with the three knob manual environmental controls. The blower speed selector only works on high speed and not on the lower three settings. I've pulled the rheostadt apart to see if that was the problem but could not isolate the failure. Anyone have any ideas? Any ideas on how much this would cost to fix?

Thanks
Mark