Heater seems to be going out and blowing cool air, especially if i turn fan on high.

Either the thermostat needs replacing or the blend door actuator under the dash is bad.

Are these typically expensive repairs or is it something my husband, who is somewhat car savvy can get a part to repair? Thanks so much for your fast response by the way!

Well checking the coolant is easy enough, The blend door actuator can be in a difficult spot to get at as it is under the dash. Wouldn't take long for someone familiar in doing this to do so.

Pull switch inside car & check little colored hoses are all in tac !