You can find good used BMW's if you are patient and willing to wait for the right deal. I got my 2005 R1200GS with 14K miles on it, an extra battery, extra windshield, extra Corbin seat, battery charger/maintainer, removable back rest, 2 expandable Vario side cases, 1 Vario top case, a tank bag, 1 inch Rox handlebar riser, removable foot pegs that mount on the spark plug cover area and 2 new tires for only $6300. Comparable bikes with more miles and less options are traditionally in the $8K - $8500 range around here. But make no mistake, it's a big, heavy bike and if it goes over with you on dirt, it would be a pain in the butt for a smaller guy to pick up. I'm 6'2" and 205 and I can do it but it's a chore.
Nonetheless, that lightweight Yamaha does sound like a fun bike and a really good choice for off-roading.