I'm very sorry your little boy is ill. I don't have any experience personally, but I've read of many pups who have done great with the surgery. This link is very comprehensive, and it explains the surgery. The cost of surgery there is less than many places, and Dr. Tobias is an expert on lover shunt. They may know of organizations that offer help for pups in need of the surgery. I would reach out to them.
http://www.vet.utk.edu/clinical/sacs...2013-09-26.pdf