first step: try direct connection to heater to be certain the heater is not working before you decide to repair or buy new one.
2) cost of repair or replacement goes with the valuation of your vehicle. Depending on you how much you like your car? would you like to replace it or not? think about it and only you can answer...
3) with the thrmostat, you have no option but to change it. Hope this answers to your question.
Ramji Patel
October 2009