I'm rushing this morning but I know there have been a few threads about this in the past. Here's one:
Budget Friendly Ideas
A couple of quick thoughts - use dried beans. Beans are great South Beach food, lots of fiber and nutrients and good carbs. They are versatile and I often eat them with every meal. Using dried is so cheap!
Buy what's in season. Around here we can get winter squash (for Phase 2), end of season tomatoes, cabbage, carrots, turnips, and fall greens for a great price. South Beach stresses veggies, 4.5 cups a day, so build your meal around the seasonal vegetables.
Whole foods can appear more expensive at the start. Most people find they need smaller portions of whole foods than they processed foods.