I personally wouldn't recommend a dimmer (or rheostat) unless your room that you house your snake(s) in has a rock steady temperature. With a dimmer it always puts out constant power at whatever setting you have it set at. So if your room cools down, then it may need adjusting, if your room warms up, it may need adjusting. Basically, you'll always be adjusting it unless the room is constant.

I'd go for a Ranco t-stat. Can be had for not that much and would be better than a dimmer.