I'm sorry but a thermostat is mandatory, not optional. An unregulated heat source, even a heat pad, can easily get too hot and burn your snake.

Thermostats need not be expensive. You can buy an inexpensive JumpStart like this:
https://www.amazon.com/Hydrofarm-Ger...mostat+reptile

Look on eBay, maybe you can get one for even less. I often seem these t-stats for $30 or so.