I'm using a 500r and I haven't had a problem with it yetI'm only using it to control 2 UTHs. Very effective and easy to use for the price. It seems perfect if you only have a couple heat sources to control and don't want to spend hundreds of dollars. I completely sympathize with you on that as well. I don't have the extra funds to buy a $150 thermostat either.
As far as your original question, I was going to say The Bean Farm too. Also, if you're looking for frozen feeders, I found this site http://www.canadianmouseman.com/eng/index.html Never dealt with them before but it's worth a shotHope this helps!! In regards to the 500r you're looking for, I'd say you're probably either going to have to order it or wait for it to come into your Petsmart. Unless someone knows of a store that has it. Very frustrating though
Good luck!!