the problem with having a uncontrolled heat source is the risk that the UTH could spike and reach harmful levels. even if it reads 90-95 on the hot side, it could possibly be hotter then that and burn the snake. not to mention that 90-95 is a rather large temp swing, and dropping to the mid 70's at night is dangerous. the least you could do is get a rheostat (lamp dimmer) from lowes for $10. this will keep the temps from hitting high levels but with fluctuating room temps you're gonna be checking the temps constantly.

if you don't have the money for a thermostat, what happens if the snake gets an RI or gets burned... can you afford the vet bills? those are going to be a lot higher then the $75 for a thermostat.