Anyway, they did not have this one in stock, but I noticed a 'regular' analog thermostat marked for $9.95, rated up to 300V-AC, and marked 'heat only' since it only triggers when the temp is above the set-point and not below it.
I went ahead and bought it since it was so cheap (turns out it was
supposed to be $18, but it was mismarked and I got it for the lower price), brought it home and hooked it up to my lamp. Works great. I don't need it at the moment because it was about 75°F today, but that's beside the point. I would have been more fun to build it out of little pieces, but... damn thermistors! I do plan to modify it because (for some reason) the thing requires 2 AA batteries.
Doesn't make sense when there is a perfectly good line-voltage source RIGHT THERE FOR USE.
Interestingly, when I was hooking it to the cord to plug it into the wall I noticed that the PCB inside was marked at the bottom with HEAT and COOL, and there was a resistor hooked to the HEAT side. This makes me think you could move the resistor to the COOL side and reverse the polarity of the trigger.
The temp range is is 50°F-100°F, so not good for lagers, but fine for ales.