IR IMAGING DEVICE on the cheap

Have you considered a cheap-ish night-vision security camera? (Not sure if they block normal daylight.)
These modules (or similar) are available with and without an IR filter. Perhaps use the difference between their outputs?

 

I've got an expensive Flir camera but alcohol works just as good for finding shorts on circuit boards.

 

I've seen some on Youtube use common old web cameras as well with a mod to remove the IR filter.
Some more difficult than others.

 

It's a common technique to apply isopropyl alcohol while briefly applying power.

Look at 2 min into this youtube video.

 

Use the IR window from a junk TV etc remote control?

 

Very much out of line. Suggest you read up on thermal infrared cameras, which are mainly sensitive to IR radiation in the 8 to 14 μm wavelength range. Silicon-based visible imaging cameras only have a near-IR response that peaks at about 0.9 μm. FLIR Corporation makes a suitable imaging camera that sells for around $300. Try this page for starters and links to more information.

There may now be low-resolution, raw microbolometer, sensor arrays available, especially from Asian sources, but good luck trying to use them. I would want to see something on the order of 100 x 100 pixels or better before wasting any of my time on them.

Most black plastic, such as heavy-duty (thick) contractor bags, are transparent to infrared radiation. You will need either a germanium or zinc selenide lens to focus thermal IR images onto the sensor plane. Ordinary photographic lens are opaque to the range of wavelengths that you need to image.

 

I would like to buy/build a thermal imaging camera for marine casualty searches, but I suspect that is a whole different ball game.

 

I suspect it is. Why do you think a thermal imaging camera would be of any use at all for marine casualty searches? Are you looking for living survivors above or below the water? If not living, then after a few hours exposure to the marine environment everything reaches the same temperature. A thermal imaging camera is "blind" to objects at the same temperature as their surroundings. Tell us what you are trying to do before concluding a thermal imaging camera is right for you.

 

you can find Flir C2's on ebay for around $200 sometimes (used)
I got one awhile back but rarely ever use it as its not as useful as I thought it would be.

 

The resolution of a C2 sucks (4800 pixels) to be of much use.

You need much higher resolution to see detail for electronics use.

Btw, If anyone is interested, I've got a Flir E4 upgraded software to E8 resolution (76,800 pixels) for sale at a fair price.

 

Its good for the price range op talked about and is in a nice small convenient unit. I see detail plenty good enough with it for repair work and considering how little I even use IR I don't think I could suggest something 10X over what the op was looking to spend.