Actively remove all references to the concept of saving money on staple foods. In the USA, conspicuously trying to save money on staple foods is a signifier of poverty. Almost nobody is proud of it. Many people try to actively hide the fact that they're doing it.
Promote the ability to grow some kind of food that's unusual enough to tell your friends about. If, for example, I were able to harvest fresh heirloom tomatoes in Maine in January and feed them to my dinner guests, that would be both good for my ego and good for your marketing. A more realistic example, perhaps, is the fad for backyard chickens: Raising chickens is fun because, every time you serve someone an omelet or a quiche, you get to start a conversation about the chickens. And the eggs make great gifts. Play up the odd and potentially fashionable.
Is there something particularly tasty that your system is uniquely good at growing? Is there something particularly hard to grow that your system makes easier?
Are the plants fun to look at? Would you show the garden to your friends?
Can kids run it? Perhaps it's an educational experience. Pitch it to school groups, community centers, local parks, science museums, children's museums, et cetera.
Can one start small and grow into a full system? "Feed your whole family on a 20-by-20-foot lot" is actually not such a great sales pitch. You ask for too much commitment. I've tried hobbies before. Most of them don't last and I end up selling the starter kit on Craigslist three years later. Worse, if you convince me that replacing 100% of my grocery bill is the victory condition, when I only manage to replace 37% of my grocery bill I will feel like a failure, which is just perverse. What you want, instead, is for me to successfully grow four plants, swell with pride, and tell all my friends that gardening is awesome.
So a better pitch IMHO would be "try this thing on a small garden and enjoy the nice fresh [insert delicious thing here]; then, if you like it, you can expand it bit by bit, until you wake up one year and find that your 20-by-20 foot garden is producing more food than your family of four can eat in a year, with almost no effort and at a cost of pennies a day."
Congratulations on being smart and realistic enough to try and find your market before you invest any more time or money. Good luck!
EDIT: Ooh, here's a fun one: Take a hint from the local county fair and gamify this. Build a social network. Turn it into a competition to see who can grow the most pounds of food in a given area, or something. It's like Farmville with real farms.