Achilles Please save my dog

Around Dec/23/2014 our dog Achilles seemed to be having issues appeared to be paralysis of the left side of his face we took him to our vet; he suspected nerve damage, at that time we treated him for  weeks with medication. (during this time we ran into issues with our youngest cat after a few visits to another vet we lost her, so at this point we were in over $1700 and our bills were pilling ). In January Achilles issues were getting worse his back legs were all over the map at times with certain movements not fully making it up the stairs, feet slipping and after slipping outside he was limping with his front left leg so off to the vet we went again. In february we did tests, blood work and my vet feels like there is a possibility he may have a neck injury. A cat scan would show us what the problem would be however, that can cost over $4000 then we would be looking at surgery that could run us over the cat scan.          My boy is my baby and I cant bare the thought of losing him. My husband is on disability leave from work and our bills are high. We are treating Achilles with metacam right now and we have seen some improvement, but I want to know what is wrong and get the surgery done. I would be devastated to lose him over an injury. All donations would be greatly appreciated and thank you everyone in advance!