I think there's a lot more risk in buying the cheap t-stats you can find in some pet stores. They have a higher failure rate and when they fail, they tend to let ALL the power through rather than shutting it off...so instead of turning off the heat, they can cook your snakes. Some people use the cheap ones with no problem...but for me, the increased risk is simply not worth it.

You can get a good reliable on/off t-stat for around $60...Ranco or Johnsons...both good brands. I wouldn't use an on/off for an incubator, but you've got that covered and the Ranco or Johnson would be fine for a rack.