D.T.
Baby steps..... first just start reading your labels. At the beginning I just used Meijers and went through their international eisle and they have Organic fruits and veggies. But some stuff you can start making yourself like homemade apple sauce, or bananna mini muffins, or snack mixes using cherrios and whatever your son likes. By not putting things like mold inhibitor and hifructose corn syrup into foods you are making things better. Pancakes and waffles that you make can be frozen for quicker mornings or quick dinners. Rice and Couscous work as good starches or to mix w/ meats. Soy Milk can be purchased as a substitute also at many stores. Work off of what he likes and sort of add to it and make it better. We also dry fruits and veggies on a dryer machine, make homemade fruit juices on a juicer and homemade breads. It won't be super expensive if you go slowly plus you have to figure out what your family likes and doesn't like. Plus some of this you can do w/ him and when they help they are more interested in the foods!
My family is not totally organic but we do try and we have made things better. I have found one secret is making as much as you can.