I hear a lot of "it's so expensive to eat healthy" in general, and then at the start of 12WBT, "it's so expensive to eat this way/cook these recipes". It is entirely possible to eat healthy, 12WBT-style on a family budget (or a single person's budget, but my tips probably don't work so well for that).
I spend about $200 a week on food and groceries for two adults and three big-eating children. I know plenty of people who spend less, but I do believe this is below the average. About half of what I buy, on average, is organic, and I try to buy ethically where possible (free-range chicken and eggs, no Nestle as I boycott them due to their shoddy marketing of formula in third-world countries, no slave chocolate - oh wait, chocolate is not 12WBT-friendly anyway, LOL).
Here are some of the tips that work for me:
1. Learn what meat cuts/types you need, and look out for them marked down or in catalogue specials. I always pick up lean beef mince, turkey mince, chicken breast, kangaroo, whole chickens, lamb cutlets and lean pork if I see them on special, as these are all used in 12WBT recipes or in my own 12WBT-friendly recipes.
2. If you have the freezer space, buy in bulk and freeze in suitable portion sizes for your family's needs. This works for meat - many good butchers will sell cheaply in bulk - as well as 'luxury' items like frozen berries. Additionally, many, many things can be frozen to reduce waste. Try freezing sliced ham, Weight Watchers bacon, ricotta cheese, milk, chopped fruit, chopped vegetables, bread, Mountain Bread wraps - www.mountainbread.com has free delivery and is much cheaper than supermarkets - homemade stock, cooked shredded chicken breast, the list goes on.
3. Do not buy fruit and vegetables from the supermarket! The quality is usually poor (long storage times, produce selected for appearance instead of quality/taste) and the prices expensive. Find a good local growers' market, fruit and vegetable shop, or even better a farmer's market. Buy as fresh as possible for eating raw, but if you're going to cook with it (e.g. soup or stews), keep an eye out for marked-down bags of produce. I get my produce delivered from www.aussiefarmersdirect.com.au due to the time and convenience factor, and the prices are comparable to the supermarket. Occasionally I go to the bulk overstock markets at Canning Vale and purchase big boxes of various fruit and vegies that I either cook up, or chop and freeze.
4. Learn about seasonal fruit and vegetables. Joy of joys, it is spring and I can finally eat fruit other than apples, pears and oranges - strawberries and cherries are coming into season! The recipes on the program don't always use seasonal fruit and vegetables, so learn to substitute. If you're new to cooking, ask on the forums for suitable substitutions.
5. The substitution rule can be applied in other instances too. Smoked salmon too expensive and you got lean ham on special? Use the ham. Have an open packet of something needing used up? Either substitute it into the day's planned recipe, or switch the recipe entirely.
6. Get to know the recipe index. Tight week? Shop from your pantry - take a look in there and work out what recipes you can make with what you already have.
In addition to these tips, remember that if you're anything like me, you'll be spending less on takeaway, dining out, and processed foods than you were before. That helps me when I want to buy, say, some cherries, which at $12.98/kg sound expensive, but I can buy a good few cherries for the price of a chocolate bar - and a lot fewer calories.