It's really hard to say what it's worth from your description. Not enough data.
The low compression might just be from a bit of carbon between a valve and its seat.
That particular bike, if in good shape is fairly desirable, so don't write it off as worthless.
These bikes can be expensive if you don't work on them yourself. Since I do, I've found them to be very economical. Once in decent shape (not perfect, just good strong runners) they'll cross the country no problem! If kept up and maintained, they last a long long time.
When a bike's been sitting for a long time it's possible for water to settle in the transmission and rust the bearings. Mice like to build nests in the air filter. And chew up the wiring as well. Tanks rust out. Tires get old and rotted.
So it all depends how far down it's gone and the asking price.
Wanted: Dead, smashed, crashed or trashed gauges
BMW GAUGE REPAIRS - TACH*SPEEDO*CLOCK*VOLT METER *PODs & LIGHT BOARD*