Herpstat makes the best thermostats i've seen on the market. they are WELL worth the money and will last FOREVER!
if you cannot afford a Herpstat, start saving up and use a JumpStart thermostat for the time-being. the Jumpstart should not be relied on as a permanent solution: they're cheap and eventually WILL fail. i have not had one fail on me yet but i don't use them long enough to find out; longest i used one was 2 years.
consider the fact that the snake will be in your care for at LEAST 20 years and the price of a Herpstat is certainly justifiable.