Yes, this gadget may be very useful.
However, $90 is a lot of money for something that is not used so often.
It has to be a low-magnification (very short focal length) telescope, with mirror - I think I have some suitable parts (
I made one RA-viewer, for focussing some time ago but I don't use it any more - live view made it obsolete), and 3-D printed enclosure for small diagonal shouldn't be a problem to design.
Webcam is probably OK as an idea, but it may prove to be not sensitive enough (if not modified for long exposures). And I personally hate to many wires around...