I built my 1970 bike from a basket case in 1983, so the dollars need multiplying by a factor of (?).
I paid AUS $800 for it,which was pretty steep, considering its condition.
The frame was bent from a collision, the crankcases were shattered, the barrel was broken, there was a hole in the primary cover, and some small parts were missing.
It hadn't had enough time in storage to accumulate as much corrosion as your uncle's bike.
Although not family, the PO was a friend to whom I had loaned the $900 to buy it in 1973.
He needed the money, and my 1972 Fastback had been stolen the previous year.
I didn't have much money to spare either, as I had just purchased a house.
My experience with Nortons was limited to not much more than setting the points gap & timing.
I hadn't built up a bike before and I wanted to see if I could do it.
Also, I wanted to save a Norton from oblivion.
I did all the work myself, except for welding up the broken crankcases & primary cover, and straightening the frame.
I spent about $2000 and had it on the road in 4 months. No internet or forum then, only the workshop manual for guidance.
Even now, some parts like pedal hangers & gearlever are painted silver rather than chromed. It's just not important.
It's the same bike, but I've changed a few things.