Please, help me save my cat (Momo)

This is Momo (Avatar: The Last Airbender reference). I've had him for 5 years now and he's my rock, my best friend, my kid, my support system, my sanity. He means the world to me. Recently, he's been limping a bit, not sitting in his normal spots and I thought it could be him adjusting to new furniture, or just stressed. Then he stopped sitting in his litter box, eventually stopped going all together, and eating or drinking. I took him to the Vet and it seems to be nerve damage and he has no sensation in his entire back half. No tail movement, can't sit normally, no jumping, can't use the bathroom.

I can't afford the specialist I need to see and it's likely his bladder will rupture or malnutrition will get to him first. I'm hoping to prevent that with this Hail Mary, because 5 years isn't long enough for me. I know the window to treat him is small, but it's there and I have to try. Thank you for any contributions.