keep looking
I have to ask: If a child had broken their hip in three places, would you be as willing to not have surgery? Sorry if that sounds harsh, but it honestly is the same type question I ask myself over my animals' care. From bad gums to broken bones, if I wouldn't put a child through it, I won't put an animal through it, whether my 'inside' pets or one of the ferals I watch over.
Start calling local humane societies and animal rescue shelters (especially 'no-kills') in your area and asking for referrals to vets who might help out for much cheaper or even at cost. I've had wonderful ASPCA vets do extensive work on ferals for pennies on the dollar.
Another option is to see if there are any veterinarian colleges in the area who'd be willing to help out. When I was unemployed and had a very ill cat that needed an ultrasound for further diagnosis, an ASPCA vet put me in touch with a local veterinarian college who did the ultrasound for free. It allowed the students to get hands on field experience with the equipment, yet the ultrasound was read by a qualified licensed veterinarian. They told me that they often will trade services, including surgery, for people that can't pay for animals that need help.
I've found that many people drawn to the animal health fields will go a few extra miles to help wounded or ill animals. Sometimes, all it takes is a little persistence and a willingness to keep asking for help.