Blood coming out of anus is NOT A MINOR problem esp in males.
Females can be in heat and have blood coming out.

Since your cat is a male, he has probably gotten into something in the garage, toxic substance is first thing that comes to mind. Bleeding from the anus is NOT GOOD.

Eventually, there is going to be blood loss and death if you dont get the kitty to the vets. A vet might be willing to work with you on the cost.