I've had uses for it numerous times and funny enough, this morning. Is the Milwaukee 2315 any good?
The 2315 inpsection camera kit is like 3x as expensive as your proposed budget in the original post. It has SD card capture and recorded photos can also be directily downloaded by usb cable to an additional device. More features are digital zoom and picture rotation along with brighter lighting
Just as an FYI though it also isn't marketed as bare tool only either
The 2313-20 (bare tool option) is at the top end of your original $150 cap.
Still Milwaukee had one other less expensive option the 2309 kit it uses a plain 9v battery just like many other off brand name cameras do.
Milwaukee 2309, 2313, 2314 all have a 9mm camera end that will fit in most any sparkplug hole, the 2315 is a 12mm camera end. Other brands vary some may even be larger. All depends on your needs
Mechanical usage...generally a shorter cable (3ft) smaller camera end 9mm is satisfactory for many people
Doing something like in construction, maybe turd hunting down a sewer pipe bigger might be better
