Go to ebay, google probeye every once in a while. replace some small rubber belts inside.
Find a dive shop, they can refill the hughes argon tanks for the joule thompson cooleras they pressure test the dive tanks with HP Argon/
About as cheap as thermal imaging gets, as low as 250$ every once in a while.
room temperature thermal really does not kick in until you get to 3.5 microns and better home ones would cover 8-12 microns.
raytheon imagers show up, but I could never find one of the 240x320 cadillac deville ones, seems most of them died before the car made it to the junk yards. I'm told once in a while a car dealer finds one on the shelf and lets them go at 2400$ each
only way to make anything decent with the most of the IR motion sensors out there is to put a chopper wheel in front of them and use them for very close targets, they are not all that sensitive and will see things just out of their field of view better then they would see a far away cold room temp target. They are piezo, and thus only respond to a AC (chopped) signal, unless you can find a newer single element or 4x4 array bolometer ie melexys.
Phil Hobbs design rocks $ for $ compared to anything else other then a bolometer chip.
Or if you can find a anesthesia gas analyser of the more modern compact kind, you can find a single element sensor with a TE cooler in the package and use a pair of galvo mirrors for scanning and and a old lens from a laser cutting shop co2 laser for the objective lens. The Anesthesia Analyser are usually 3-8 microns or so, but need the cooling and a bias current and a chopper wheel, they usually have dichroic filters on a chopper wheel for optical adsorption bands for each gas. I've picked up the modules at my local surplus place for 50 cents from time to time, and mine are not for sale.
Steve Roberts