It depends on what you want, do you want a digital read out or as long as you can see a number. Digital readout will run you 20 to 50 or you can go to the local pet store ( pet smart ) and grab one of the stick on ones for like 3 bucks and are just as accurate if not more. Just stick it about 1 inch above your substrate level and on the side of your tank or you can go for a controller system with Temp. probe and that way you could be halfway over the Atlantic and your phone can notify you that your heater is not working and your temp has dropped to 68 or has stuck on and your temp is 98 and you can't do a dam thing you can do about it but at least you know and start planes on your new system when you get back.
Whatever you want you are covered 3 bucks you're covered, 50 bucks you're covered, 350 bucks you're covered, 1300 bucks, you're covered. Just pull out the cash or Visa card you're covered it's all up to you, what you need or what you want.
Ah you got love Reefing.
Oh ya, hide the receipt and you're covered.