Found this the other day on youtube: Boss PS-6 Harmonist Pitch Shifter Guitar Effects Pedal

The pitch shifting part I could care less, what's cool is that harmonizing part. But being a broke college student, $150 is a heavy price tag, so are there any preferably software or hardware effect pedals that'll have a harmonizer effect but hopefully for cheaper or works with garageband?

- Strandberg OS 7
- A cheap fender strat knock-off not worth naming
- Garageband
- Boss GT-1
- Potato
Pitch shifting, especially harmony, software is kind of expensive. You can cheap out but you will likely notice it in the sound quality. The first pedal that comes to mind is the Behringer US600. I also had a Digitech RP-155 that did harmonies okay, you might could find a similar unit used for cheap. What you want to look for is the ability to select the key you want, and the interval you want (typically a 3rd above). If your main use is to record, you are much better off just recording both lines separately.
Amplitube's free version comes with the ability to buy individual amps and effects. Their harmonizer is pretty good actually.