If you can achieve the required hot side temps with just a UTH it would be the preferred way to go. I keep my hot side at 90-92.

This can sometimes be hard in a glass tank depending on the ambient temperature of the room the tank is located in. If this is the case you could insulate the sides of your tank with foam board. This will help your temps and provide added security to your snake.

A rheostat is ok to control your UTH with but if your room temps are not stable you will get unstable tank temps as well.

If 60-70 dollars are in your budget I would recommend a Ranco or Johnson on/off thermostat which would provide you with much better temp stability. A good thermostat is the best investment you can make in this hobby.