I think you're incredibly light on your prices. For instance, I saw one vertical fin for 300, but she looked a little crusty. Most are around 450. But that doesn't include shipping or labor to remove and replace or paint to make it match, not that it really matters. Whats shop time to replace the fin? I'm absolutely 100% for saving as many old birds as possible. But I don't think we're talking 1500. I definitely think it's worth getting an opinion on if it could be repaired vs a fuselage replacement. As bad as those few pictures looked, it was like they gave it a bath with chloride while they were plowing Quogue. If it were me. 1) get a second opinion. Particularly a shop that has done this work before. 2) Call pre-buy AP. He's probably the least culpable depending on what he was contracted to do. Find out how it was missed and why. Maybe give him a some insight on where to look next time. If I did the pre buy I'd be giving your money back. 3) call the previous owner or owners. Feel him out. After all, he sold you a lemon. Does he get evasive? That would tell me he knew. We already know the owner A/P had to have known and either didn't care or was trying to make a buck. It's interesting the engine seems ok however. 3) call previous IA's. See why/how this was missed. 4) Contact your FSDO. They're probably going to want to see the airplane and figure out why so many missed this. 5) depending on the answers above, get an attorney. If you get the sense they knew and were deceptive, you might get a judgement. Doesn't necessarily mean you'll see anything. And may cost more depending on what lawyers get.