Adrian,

This stuff can be made to work down here.  There are lots of auto steer units running in Georgia, similar topos to yours.  I "heard" that Georgia has more auto steer tractors than any other state except for Texas.  Crisp and Dooly counties have base stations all over the place, part of their "empowerment zone funding".

The kicker is going to be your differential base station source.  The cost of the auto steer system is in reach, but with that put on top, it's rough.

One thing about having your own base station is that you can move it to where you need it today.  The first time you set it at the point you need for that farm-field, it may take a while, but when you go back the next time, drop it right on the "same fence post" and you're up and going. 

I like the cell phone differential, but know little about the logistics of putting it together, or where a source would be available for you.