If I remember my model numbers correctly, the 783 was a tubular feed, .22 winchester magnum rimfire (WMR). I have a 782, which is the .22 WMR, detachable magazine fed version. The rifle shoots better than I can. I have had trouble finding scope mounts which will allow clearance for the bolt handle on some of my larger scopes. The trigger pull was heavy with a LOT of over travel. "Basix" makes a drop in trigger that will mitigate some of those problems.
Gun prices vary so much from region to region, plus things are so crazy right now that it is hard to comment on the price. I have seen versions of this rifle, in good condition, priced from 150$ to 180$ in my area (arizona), and so I think the sellers asking price of 100$ might not be out of line, depending on the rifle's condition.