Niš is a very walkable city, but if you have a lot of luggage, it's winter or you're just lazy and unfit, the buses are frequent, fairly reliable and very inexpensive, from 30-60 dinars (about 30-60 cents) depending on the zone. There aren't too many Yugoslavian sheds from Tito's time still roaming the streets, which is more than can be said for the cars in the city. Tickets are always bought on the bus from a conductor, in cash of course.