Originally Posted by Spring_Chicken
Can you post a link to the 'slightly cheaper single stage units'?
I'm not him, but if you search "aquarium temperature controller" on ebay, a lot of items come up, including SS single stage 120V units like this one:Digital Temperature Controller Thermostat Aquarium 120V | eBay
Note these only handle 5A on the relay, instead of the 10A the "standard" ebay temp controllers can handle, but if you are using it to drive a RIMS unit, you SHOULD be using the relay contact with a wall wort to fire an SSR that will be controlling the RIMS unit, (if electric), or running whatever voltage through it to run the coil on a gas solenoid if gas powered, you should be fine. (holy run-on sentence batman!)