Something to consider is the condition and size of the overhead doors. If they are in good shape, that might be an indicator of how much to offer. Maybe a maximum offer could be a fourth or a third of the cost of new doors that size.
I would guess that trusses for a building of that size may require a crane (or tractor with a tall front end loader) to get them down. If you don't have one, that could be an added cost.
What I would do is call a house mover and try and get an estimate on moving the whole thing intact. I have seen pole buildings that have been moved, so it can be done.
The most important thing to consider, is it in good enough shape that you won't regret it or that wife won't complain everytime she looks out the back door. If she hated it, that would cancel out any savings that you would reap, and she most likely would never let you forget it.
If you are happy where you live, and you plan to stay there a long time, I say build new.
