I made things work with a rheostat for awhile.. in fact nearly six months. unfortunately i never had stable temps. It would fluctuate a degree or so but if G*d forbid anyone touched the little tab that controls temps i would be on egg shells in fear of my temps spiking... thankfully we never had a problem but I know now with having a thermostat I no longer worry about that accident waiting to happen. my thermostat will shut off should the temps go above a certain degree (That i get to set) while some people can make things work using less it isnt ideal. IMPO if you cant afford to get proper equipment (im not saying in a day, but within reasonable time span) then you have no business having the animal. what happens if an unforeseen event happens (illness for instance, or burning because of faulty equipment) can you afford to get your animal to the vet?

I hope you can get those temps under control soon