I certain that's a bigger repair than $2500. Those end cap panels alone will cost more than that - then there's the labor if you aren't able to DIY.
I'm counting five (5) compound curved end cap panels that need to be replaced. I believe those panels need to be ordered & replaced through a dealer from Airstream or the trailer could go to Jackson Center for the repair - you might want to give a dealer a call to see how much the repair would be - they should be able to give you a ballpark from the pics.
* The ad seems a bit odd - why can't he sell it in FL?
* What is a bonded title? Can the trailer be insured with one?
* I also wouldn't count on his "the floor is marine plywood" comment - I don't think so. Depending on how long it has leaked, it could have floor damage...
* I would ask the seller exactly where it is and go look at it before bidding at the very least - then take more pics for a real
repair estimate from a dealer or authorized Airstream repair shop.
Just my 2-cents...