I think that if we brought him back to the rescue, they were going to take care of him and his costs (although they weren't real clear- they just said that the vet had specialized in the surgery in school and that they would take him back) However, I did some looking last night, and I know that the Yorkshire Terrier National Rescue has a fund set up for people who need assistance in the surgery costs (
http://www.livershunt.com - there's a link for requesting funding)