It's not too expensive at all. If you do it through ticketmaster, depending on which venue you're going to, it might cost you a bit over $20, like he already said.
If you have a specific venue in mind, and it's not too far, I would suggest you try to get tickets through them instead. Chances are they'll sell them a few dollars cheaper and without the stupid $5 service fee (some venues don't sell tickets, though)