While I can't help with the financial part, I can tell you that my Onyx had her tieback surgery when she was 11 and lived to 15.5. I wrote an article regarding her living with LP and it's in this coming summer issue of CG magazine.
She had a wonderful life and passed away not from anything with LP.
Also, financial wise, Care Credit allows you a specific time frame (depending on the price of the procedure) interest free. If your vet uses Care Credit, I'm thinking you should have at least a year interest free. (just transfer to another credit card if you can't pay off by that time, you'll get whalloped with high interest rates and may have to pay interest for the whole year you hadn't. But, if you play by the rules with them, they are a godsend.
Good luck with whatever happens.