As far as thermometers...I got an acurite from wal mart (hardware department)...I can't remember how much though...wasn't very expensive.
I don't know about getting a thermostat from wal mart. If you look around the forum there is a thread for making a rheostat using a light dimmer, and can be made for pretty cheap. But I don't think you can get a decent reptile thermostat from there. As far as cheap, but somewhat reliable, thermostats go...I've found that the Ranco etc111000 is widely used.