If your room temps fluctuate at all you will have problems with the dimmer. Just save yourself the trouble and buy a thermostat. It is worth the money.
Oh alright im considering the Repti500 (its 30$) more of my price range I believe, and would it be better to get an acurite thermometer or use the infrared "gun" thermometers?
On a side note: is it true that for cornsnakes a dimmer is ok? ( room fluctuates 70F daytime-60F night time)