I'll leave it to others with better links to answer that, but first you need to read Dr. Atkins' book. That's the key.
But, in my experience, you certainly do NOT have to buy a lot of prepackaged (especially Atkins-branded) foods to do this diet. In fact, I only buy Atkins ice cream (because there are no competing brands in my area yet), low-carb bread from an independent baker and Carb Solution snack bars.
The packaged stuff is really way, way too expensive, especially the Atkins brand - competition hasn't really appeared yet and the demand is huge.
The good news is that your supermarket supplies everything you need for the diet in the dairy, meat, frozen and vegetable/fruit departments. You don't need the packaged stuff at all.
And you can make your own substitutes for goodies for much less. For instance, I bought a Liss cream whipper, some NO2 cartridges and I make my own zero-carb, no-sugar, flavored whipped cream with Splenda and sugar-free Italian syrups. Great on jello, Atkins ice cream and especially fresh strawberries. And my friends had never tasted blueberry-flavored whipped cream before - thought it was great!
Read the book, give it a try - you'll find it's a pretty easy dietary change . . . . not a "diet".
They look at you funny when you buy those? FYI--in a pinch, they are most likely available at your local adult book store.