I had to read through the whole thread to truly get an understanding of what was being asked. Last time I didn't read through and posted something that was already mentioned. I apologize if this is still the case.
As far as nobody offering a cheap sensor, keep your eyes on the i3 Thermal Expert V1. They are looking at around $2000 for a 640x480 sensor, which in my opinion is very cheap for something that clips right into your smartphone. The price could come down on this, the 320x240 sensor they offer right now is the absolute cheapest smartphone based thermal imaging camera for the resolution, and it's a VOx sensor. They quoted me around $700 or so, which for a 320x240 sensor is dirt cheap for what you are getting.
Now, like everyone else said, you can interpolate the image. Try some super resolution tricks to make the image bigger and higher resolution. The reason you can't get *good* thermal images that look like an HD camera is because the thermal pixels are larger than visible light. You can't make a pixel the size currently used in visible light cameras and expect it to work. It isn't sensitive at that point, 8-12um is the range used for thermal. Visible light is in the 350-900nm range. That's *NANO*, not *MICRO*. Manufacturers can push the limits on pixel size for visible because visible light is such a short wavelength. Heat needs bigger pixels, and special processes to even build the sensor. It uses exotic materials (highly expensive stuff!), and the lens must be made from something that can pass thermal energy (germanium is the best, and most expensive). Higher resolutions means bigger sensors, which means bigger lenses. All these costs add up. FLIR and Raytheon have made great strides at shrinking the thermal pixel down to its absolute minimum for absorption. This way they get more sensors per wafer, and can use smaller, cheaper lenses. It cuts the cost for the consumer considerably. When you do this, you give up sensitivity, just like on your $50 webcam which probably doesn't work for shit in the dark (because everything is pushing the limits for cost). Seek Thermal's camera uses ZnS (usable, like comparing glass and plastic lenses), on a camera with a very small pixel footprint. No wonder it performs horribly, and all the pictures from it look like someone rubbed jelly on the lens. What do you expect though, from something that has a pixel pitch just barely large enough to even absorb thermal radiation. At least it's cheap.
tldr; What you want, you won't likely get. It's like telepathy. It's nice in thought but you aren't going to get it anytime soon, if ever. Use software tricks to make your low res sensor look like it's bigger.