It doesn't sound too bad up front. The price you have to pay for the bike is important but maybe it's helpful if I tell you that in general owning a vintage motorcycle, BMW just being one of the better examples, is a money loosing proposition. You will spend 5 or 6 thousand dollars to ride a 3 thousand dollar motocycle.
What color is she?
If you give a few pictures we might do better on assigning value.