an IR camera? I use FLIR, they can run about $2500 - 10k for house inspections. You can probably get away with the 2500 as you don't need high temperatures. I recommend taking the level 1 class to understand what exactly your looking for.
This isn’t a recommendation for an inspection camera. More of a DIY trick for those of us that are too cheap to buy a dedicated unit.
I have taken my smart phone and attached it to a 5 gallon paint stick with 4 or five strong rubber bands. It’s not as small as a probing camera but lets me see back in some places I can’t get my head and it has built in light source also and instant playback. Takes about a 3 inch opening though.