Combine wreckers have been known to pick these at auction for as little as $2500 complete with header and pickup, but it depends on the local market. I would definitely not go over $5000 on a real good one myself.
The combine wreckers are full of older 760's, and don't even pay 2,500 anymore, more like 1,500 tops. I'd say if you like the machine, pay no more than $2,000. You can sink $10,000 easy into these and still have a $2,000 combine.