I search for stuff like that from time to time for years now and all i got currently is this:
Conventional Endoscopes, which would fit perfectly as they are made for such stuff

are by far too expensive for people like us. One of the cheapest systems i know costs roundabout 10 k$ and is originally intended for industrial use. Medical units seem to range about 20 K$ and more.
Alternatively, i thought about building my own one, but that's probably tricky.
- I thought of using one of the better finger cams, one of those that have a macro-function. Such are pretty effortable, good and small (!) models can be obtained around 200 $.
- Illumination could be realized by LE-Diodes or IR-LEDs, these are another few bucks .
- The encasement is again is quite tricky, i'd prefer very soft, gel-style platinum-catalyzed silicone as i have a source for that stuff. Material costs would probably tend to 50-100 $.
- All the optical stuff has to be encased in a dry environment in order to avoid fogging of the front lens. That's one problem still to solve, probably by another front lens made of polycarbonate.
- Additionally, i'd add a vented hose to inflate air, as imaging and navigation otherwise will be unsatisfactory.
Possible problems one can think of:
- Fogging of the camera front lens if there is trapped huminidty in the system (either from manufacturing or usage)
- Break-through of signal lines or air-hose through the silicone mantle. Proper fixation of that stuff is as important as difficult and gets even more difficult, the longer the device is planned.
So i think, all that stuff should be solveable with roughly 300-400 $ if one doesn't need several attempts

In the end, the cam could be shaped like the colon snake or colon aconda (which in my opinion is kinda too thick). But planning and working on such a project is quite time-consuming, and that's pretty most the thing i am *really* lack of.

But we could try to realize at least the planning part here, maybe someone then is interested in building one...
Best regards,
Thrawn