The bus in Salzburg costs 5 euros for a one day ride if you just hop on the bus. It is outrageous but that is to catch the tourists.
Here are some options of cheaper tickets if you go and buy your tickets at a Tabak Traffik instead of on the bus:
Tabak Traffik 4.20 Euros
On the bus: 5 Euros
Single Way Ticket:
Tabak Traffik 1.80 Euro
On the bus: 2 Euros
But it can be cheaper if you buy a 5 packet of single one way tickets. I can't remember how much cheaper but it is a better deal than to buy them individually.
I only bought a few day tickets and some one way tickets as I walked almost every day to class. But for those of my classmates that lived on the outskirts of the town and had to take a bus they would buy weekly or month passes. The one catch with a week or month pass is that if you lose your ticket you are out of luck, but the up is that you can ride for as much as you want on that ticket within the time allotment. You can buy them at the Tabak Traffiks also.
You want to BUY a ticket! It can be pretty tempting and easy to just hop on the bus but the Austrian bus patrol people are serious. They are not always wearing a uniform and could just start checking for tickets. It is a 60 euro fine if you are caught in Salzburg and if you don't have the money on you the cops will walk you to an ATM.