I've just completed the design of a stupidly cheap thermostat that is capable of regulating the temperature of DIY incubators to within a few 10ths of a degree. I did this after having no end of trouble using a traditional "oven" thermostat from China. which had a range of 32-40 C on the same setting! The design, while strictly for those who are moderately competent with a soldering iron, is very easy to build on strip board and uses only commonly available parts that you can get from a local electronics store or eBay at a pinch. I'm happy to post details here with the strict proviso that it does switch mains (110-240) voltages for the heater - such as a 60w bulb and it should only be attempted by experienced builders who are capable of such wiring without endangering themselves or others. The controller only employs 12v but has to activate a relay (just like a conventional thermostat) so I want to make that clear. If everyone is happy, I'll post the circuit and parts list here later.