Here's what we use:
Terrycloth washcloths: washing children, dishes, counters and floors (not all with the same one, though!)
Terrycloth hand towels: drying hands/children, drying really wet things that don't get linty
Flour sack towels: drying dishes that do get linty, covering rising dough
Cloth napkins: used at every meal, also sometimes stolen by children to clean up their own messes
Microfiber cloths: cleaning electronics and eyeglasses
Cloth diapers: cleaning up floor accidents (then thrown in the diaper pail with all the rest)
Cut up pieces of worn-out tshirts: used primarily for cloth wipes, also for cleaning random things and wiping noses. If the thing to be cleaned would ruin the rag (like paint), we compost it if possible or throw it away if not.
Paper towels: soak up kitchen grease, really gross clean-up stuff. Again, composted if possible, thrown away if not. (We go through about one two-pack of up&up make-a-size towels per year.)
I don't think you can accurately assign a cost of washing reusable towels/cloths. I wash something from one of the above categories in virtually every load, but they just go along with laundry you would do anyway. Like, if you load up your washer with all your clothes, and it's mostly-full, you could still throw in a few napkins and a dish towel and run the washer with no extra cost.