Do not spend $25k. Chances are that the wood is pressure treated and should not be in too bad of shape. Like the earlier suggestion, you can just slap some new sheeting on top of the old. You could even do it all the way around the pool (if it's real bad) which would likely mean that you'd want to put some new bead receiver at the top of the wall, too. You may have to deal with some new fittings for your returns and skimmer but that shouldn't be too hard. Just don't let some Joe Blow pool guy come in and tell you that you have to do this or that. He'll just be looking to make a quick buck.