welcome Joe,
Even if you have been off the road for a long time, riding a bike is like riding a bicycle. You never forgot.
After 15 years off the road, when I picked up my first K75, I rode it home for 1,300Kms in a stormy day (high wind and rain). I was extra cautious but I didn't have any problems. The same with the sidecar.. I didn't ride any for 30 years and when I went ot pick up mine in the USA, I was very apprehensive. After 5 minutes retraining in the parking lot of the motel, I was feeling comfortable to ride it home to Canada.
About the K100/K75, they are very reliable and easy to work on. If you sift through the forum, you will find a lot of people not being mechanically inclined. With our help, they never visit a mechanic and do their own maintenance. Brad-man is right about buying a bike which has been off road for many years. They can have problem, but this is the same for any vehicle. The rubber/seals will dry and they will have to be replaced.
I was just looking at what is available in Canada:
Kijiji Canada (the equivalent of the Craig list in the USA)This gives you an idea of the asking price. (Don't forget, the prices are in CAD $ and the US $ is something like 25% higher).
Before you buy a bike from anywhere, get the maximum of information, take a lot of pictures and speak with us. We will wisely advise you. BTW, most of the times it is better to pay an extra $1K for a bike in excellent shape than having to put this money later to keep it on the road.
Good luck with your future purchase.
CF