Looks like Archie has given you quite a few to check with. I'm sure there has to be something on that list that can help.
Just please, don't put that baby down. If all else fails, then let United Yorkie Rescue have him.
United Yorkie Rescue
If you do find a way to get his operation, keep in mind that he will not be able to run around for 8 weeks till the pen is removed. I hope you can be home with him or take him to work with you, or even have a friend and/or family member help you out.
As was mentioned before, you could sell your car (NEVER trade) and get one you can pay cash for and still have money for the surgery. That's exactly what I would do in that situation. Doesn't sound as if you should have a car payment right now anyway. Go on line to Kelly Blue Book and see what your car is worth. Never buy a used car from a dealer either. Always buy from the owner and keep in mind that everyone ALWAYS list's the car a few hundred dollars more than they actually want.
I want to say good luck to you and you do have other choices rather than putting your baby down.