Actually those inspection cameras are pretty cheap now. I bought one just to have, and it works real well. Do not remember the price, but being cheap it was not too expensive. It was a "just in case" purchase. I would bet I paid less than $50 delivered, and it has a fairly high resolution camera...1080p I think...
I got one for twenty bucks. Don't know the resolution, but it's good enough for this kind of work. Takes pictures and videos.