Total cost for Amplitube was right about $50 (cost me $20 for the app, about $30 for the iRig adapter). It just happens to have effects built in. You also don't have to use other handy built in features like a presets, a tuner, metronome or recorder... it's just all there in one handy app. There are free and Lite (LE) versions on the iStore too, if you want to explore it a bit before actually shelling out cash.
If you're absolutely against effects period, there's also Gallien Krueger's [Invalid or Expired Link Removed], another iOS app (and I have this one on my iPad as well). The iRig adapter works for this app, but GK also has their own version, the [Invalid or Expired Link Removed]. Again, you can jam along with tracks on your device. Again, this app has a free version as well, full version is only $4.99.
Just making suggestions based on you saying you're looking for a headphone practice rig and you'd already be using an iOS device.
I haven't gotten either one to work in a live situation yet, but have only tried once... I've heard of people doing it though, so I may give it another go.
EDIT: The practice rig I actually use at home is a Line6 Toneport UX1 with Podfarm.
5sg.
If you're absolutely against effects period, there's also Gallien Krueger's [Invalid or Expired Link Removed], another iOS app (and I have this one on my iPad as well). The iRig adapter works for this app, but GK also has their own version, the [Invalid or Expired Link Removed]. Again, you can jam along with tracks on your device. Again, this app has a free version as well, full version is only $4.99.
Just making suggestions based on you saying you're looking for a headphone practice rig and you'd already be using an iOS device.
I haven't gotten either one to work in a live situation yet, but have only tried once... I've heard of people doing it though, so I may give it another go.

EDIT: The practice rig I actually use at home is a Line6 Toneport UX1 with Podfarm.
5sg.