[bigben2k]

Bill's right; eBay has chillers, be patient. Plenty of Thermoteks right now, but averaging $500 (they used to go for as little as $150).

I've explored the alternatives around a chiller, and they're not pretty;
if you're not able to sustain a specific temp (as a chiller would), then the only option left is to try to maintain a steady temp slightly above room temp (i.e. 25 deg C). So you integrate a thermal probe with a PID temp controller (preferably a smart controller), to vary the radiator fan speed... long, complicated, and will only work with the right controller.

Thanks for the comments blue68f100; you're spot on about resolution and response time.