My cat Wilbur

Hello, my name is Rico and one of my two cats named Wilbur has been very lethargic lately. At first I thought he was scared because he went into hiding under my bed when a lot of family came over, but now he’s been hiding under the bed, in the litter box, or sometimes in his cat tower. He hasn’t eaten for 3 days now and I am trying my best to get him to eat. He has been drinking water. He had a previous ear infection too that I thought went away but now I’m questioning if it has a role into why he is acting like this. He recently was not able to properly walk and it looks like his back legs are giving out. I want to take him to the vet and see what’s wrong with him but it’s so expensive, especially if we find out he needs surgery or any other work done. Please help me, this is my first ever cat and I don’t know if I’ll be able to help or save him