Save Shadow's legs!

This is our 4 and a half month old golden retriever puppy Shadow. He has been a part of our family almost 3 months now. In the last few weeks he has had great difficulty moving his back legs, and even walking or sitting. He was diagnosed with a possible blocked neural receptor. His bill is already 350 and this is before any treatments. This means the difference between him having a chance at life or having to be put down. I am a single dad with two little girls and full custody. I work full time as a server and have very little extra monthly income. My girls and I have become very attached to our little shadow as he is the first pet we have ever had. He is a sweet dog who loves belly rubs, drinking water from a running faucet, and playing in grass. We are asking for any help that you can give to save our fuzzy friend. I thank you and God bless.