The cost of the tune will depend on a few factors - Access port vs. open source, speed density vs. MAF, remote tune vs dyno tune, etc. Depends on what your expectations are and what tuners are in your area.

If you've got a relatively stock engine and do a remote tune, that might run $300-$400, a dyno tune may be $600-700 rough ball-park. An open source tune will generally cost more than an AP since the AP can do on-the-fly changes, then again it will cost you $500-700 for an AP. In my case, I wanted a speed density dyno tune and couldn't find a tuner in my area to do that open source so I had to break down and pick up an AP.