You won't be able to use GSnap very efficiently in Audacity. Audacity only supports destructive effects, so you get one shot at adding the effect. While this is not recommended (at all) it can work alright for chorus and reverb if you're absolutely sure it is what you want (cause you won't be able to change your mind later). But with pitch shifting, you will definitely need to be able to make further adjustments. Because how it sounds at one point in the song can be completely different at another spot. Pitch shifting is best done in real time, so you can make adjustments as needed.
IMO even automatic pitch shifting (which is what GSnap does) isn't very good (I have used GSnap and really didn't like it) but if it must be used, it's far better to use it in real time.
$40 for Reaper and you are on your way.... and you can try the free (unlimited) demo version to see if you like it.
I also have a tutorial for loading VST effects into Reaper:
Reaper Tutorial
-tkr