Really, do yourself a favor and get a Herpstat. With the money you have spent on cages and RHPs so far, don't cheap out on the most important part. The cheapest Herpstat that can be had is the intro or intro+, which are $100 and $110 respectively. I'd recommend the + as it has a hardware safety relay in case something goes wrong. I got mine from GLK herp which offers free shipping (http://www.glkherp.com/).
Being able to set the temp and know that it will be actively monitored is completely worth it, especially if you have a cold room.