I'm a working mother of 2 with a husband that doesn't stop eating so it is not hard to imagine that we can actually go through the larger (and ounce-for-ounce) cheaper bags of spinach, apples, carrots, etc. However, by purchasing a few staples in bulk rather than a variety of small packages, I've been able to save a lot of money and still eat healthy! Also, this should go without saying, but don't let food go to waste. Sometimes my motivation to eat a salad rather than a few spoonfuls of peanut-butter is simply that my veggies are going to go bad soon.
I also cook several gluten-free meals on Saturday for the upcoming week after I've gone to the market. I find that planning our favorite meals out and shopping in bulk has saved more money in gas from the many trips running to the store for every little thing I might be out of.
I didn't become an expert meal planner until I was diagnosed with gluten intolerance now my whole family is eating better.