We are going to use them in a warehouse environment for order picking. This will be on smooth sealed concrete floors to pull stock down from higher racking. I am assuming there are two drive motors? Approx. how much does a new drive motor cost?

the wav has not changed a lot since they first came out in the late 90s, in fact, a drive motor update is all I am aware of as far as changes (but I don't work for a Crown dealer since about the time these were new, but I do care for a few)
800 hours sounds not too bad, it is my guess that they will need new drive motors, as this is the weakest spot in this design, in my experiences. and the drive motors are not $ friendly.
I think I would ask about the reason you think you might want one of these, their usefulness/design is limited, and not good unless the floor is pretty close to level and in as good a condition as in a retail environment, where a lawsuit from someone stubbing their toe on a poorly fitted floor tile would be a di$aster.
As I understood it, their design purpose is to reduce the number of ladders in a retail environment, not so much to be a go-cart/golf-cart/bicycle replacement or to drive in an asphalt paved area.
800 hours is about what most owners of wavs report as the top end of the drive motors useful life,