12 volt winches are neat (unless you've a 6 volt bike), but they pull a lot of amps. Doubt many dirt bike batteries could power them.
Deer winches might be a far better idea. 700-1000 lb compound pulling power, and typically upwards of 100' of cord on them.
Added: Here's an example. At that price, I might quit looking for my lost one, even if the lost one is a wee bit smaller.