Inavailability of bare sensors is the problem here. The FLIR Lepton sensor alone costs about 50% more than a Thermal Master P1 - which is a complete camera with the same resolution, better range, and works with a variety of apps.
The bare sensors used by Chinese companies are probably much cheaper, but I have no idea where you'd buy them.
Thermal cameras from far east are much much much cheaper and capable (=higher resolution up to non-interpolated 640x480 without selling your kidney) in 2026.
It's kind of crazy the sensors are so expensive to buy off the shelf compared to just getting a full thermal camera.