Cat question?

I have a cat named "flippy" and she has always been in good health until just a few days ago, when we noticed that her hair is falling out!! right above her tail like on her back bone. It was a small patch at first, but now it seems to be getting bigger!! the spot went from the size of a golf ball to the size of your palm!! we are soo low on money that my dh refuses to pay for a visit to the vet...so I need to see if anyone here has ever seen anything like this? It really looks like the "hot spots" my dog use to get years ago...but she is a inside cat. It doesn't appear to have any broken skin, just missing hair..and it's in a place where she can't be scratching it off. is there anything I can buy over the counter that will help her?
TIA
Mollybee