I'll be moving out next year and I'd love to adopt an adult cat from the humane society. I'm just wondering how much a healthy cat costs. I could sit here and add up food, vaccines, etc. but I don't know how much little things like litter cost each month. I'd prefer to have an inside cat even though cleaning litter boxes is one of my least favorite things to do at work. I'm just afraid that my cat would get hurt roaming free outside (maybe one day I'll own an inside/outside cat, but having never owned a cat before I'll be too worried about it outside ).

So, how much would you estimate a healthy adult indoor cat costs each month?