I, too, am looking for an inexpensive GTD software solution for iPad. I have been looking at Get It Done and a few other.
First, a general comment: it seems like many, if not most, of the creators of "GTD" software have never read the book! They are missing elements of the GTD methodology or major disconnects.
This brings me to Get It Done:
I was initially confused by the Areas tag. At first I thought it was what GID calls contexts, but then I was confused when a project was assigned to an Area and you if you signed a task to an area, you could only assign it to projects that were assigned to that area. As I read more I discovered that Area is a general category of tasks and projects, such as "Work" and "Personal." I can see that potentially being a useful division, but is it really? I don't remember GTD encouraging use to separate tasks into Work vs Personal, etc., just into context, which Areas does not work for.
In
Get It Done Setup the creator suggests that Projects are the equivalent of contexts. What?!? That makes no sense! He advices that one sets up a Phone project and put all phone-related tasks under that. Where, then, does one setup the projects--the open loop--one must store? Using Projects as contexts loses the vertical integration of tasks in a project.
One way I came up with to implement contexts is to set up the contexts as tags and create Smart Groups with those tags so I to pull up all the Phone-related tasks, for example. I'm not sure I'm happy with this method. I would prefer it if contexts were supported more directly and less obtrusively.
In addition to these GTD-method disconnects, $39/year seems a bit much.
I haven't tried Toodledo and related mobile apps yet, but that appears to be my next stop.
Peter