It seems like a decent deal. You should checkout the MPU board. If the batties have leaked on the MPU board, that could get expensive to fix. Unless you are familiar with fixing the boards, then it's just your own time being spent. So you should take a close look at the battery pack and be aware of what you are getting yourself into.
The other thing is while you are looking at the MPU, look around at the other boards for board hacks and burnt components.
Also the ramps should be in good shape. Those get expensive to replace, if you can even find them.
