Whoa~ That is the most expensive quote I've ever heard for LP surgery
You may want to get another opinion if it comes down to that.
The best preventative would be probably to not ever let him jump up/down from any kind of height (bed, sofa). Hopefully he'll never need the surgery.
Good luck with the breeder, I hope that she offers something fair for both of you AND that she won't be breeding that pair again.