three cats is almost no more money than having two...expect for the initial vet bills.
UNLESS the cat has feline herpes or some other disease that will require vet visits and meds and the time to give them the meds up to maybe 4 times a day.
I really am not saying you shouldnt take the kitty in, I know I would want to, but just think of that first. the humane society could help you maybe, with where to take the kitty for low-cost neutering and shots. and there is the a.r.f (animal rescue foundation) the f.a.i.r. foundation and the hermitage, all no kill shelters here in Tucson. maybe they can help you place the cat...
of course it would be great if you could keep the kitty but sometimes as much as we want to we can't. this is a hard subject! I would want to keep it too!