Hind leg paralysis in Maltese breed dog

Well last week my Maltese dog(9 years old) was running after a cat and then suddenly slipped and flipped on his back, after 1-2 minuets of squealing and continuously wagging his tail he stopped making noises.We brought him inside and and we noticed that he had lost sensation in his hind legs
after a while he even lost control of his tail. We took him into emergency at the vet, his immediate reaction was that he must have broken his spine or neck (symptoms showing were stiff hands
stiff body
weird posture
stiff neck)
but when the xray came up it showed no signs. Then the vet said that it must be a strong muscle cramp and gave a tablet and a a medicine(petcam).....now he cannot use his hind legs neither can he use his tail,he drags himself all around the house regardless of the position of his legs

please give some advice on his recovery and/or if anyone has had the same case before.
looking around on the net we found dog carts but they are expensive , so i was looking for a second-hand dog cart.

Regards
Sanjay