thermostat problem? What would be some other problems to look at and what would an estimate be to have it fixed?

drain your rad.get one gal. of white vinegar.pour intorad.,and run car at an idle for 15 to 20 minutes with heater on.then drainrad.again,and flush the rad.with water for 10 minutes/stop and fill rad. with antifreez/coolant.this should fix your problem.it could be a stopped up heater core.