I had 81K Miles when I sold my 2002 M5 this summer. It had NO Vanos issues and didn't burn oil, and ran perfectly. I would NOT buy a 2000 or 2001 model, which were prone to oil burning, carbon deposits, and Vanos problems.
The guy who bought my stock M5 has invested about $20K in upgrades, and runs about 650hp (supercharged). No problems so far...but I wouldn't typically recommend this on 81K mile car. As for price...lower mid 20's is about right for good to very good cond.