Buy cheap you get cheap, and possibly melting flexwatt which in turn burns your snakes and creates even more money spending in the form of vet bills(or dead snakes from overheating). OR a burned down house...
Get a Johnson Controls or a Ranco. They work just fine and can be found for $65 to $70 depending on where you buy it. Sometimes as low as $50 unwired.
Do not buy cheap or you will regret it. Not a matter of IF, but WHEN. And that "when" could be when you're not at home to prevent the problem from happening.
Even a JC unit will turn all power off to the flexwatt if it gets too hot. None of your cheapo units will do that.