It won't save the world, and it won't save a whole lotta money, but let me extol the virtues of using whatever little space we city-dwellers have for biointensive container gardening.
It attracts birds, which are also cheap fun.
If you start real early, you can grow from seeds which makes the operation almost free, from a money standpoint. (Time, of course, is another matter.)
The time we spend watering and otherwise nurturing your plants and the soil they grow in is therapeutic. Container gardens are therapists that work for free, and let you hold a beer while working on your mental health!
There are a lot of little corners that are better off with something growing in a pot. Look around! A sunflower need very little space, and yields amazing results.
This year, I'm trying to grow everything from seed (although I did invest in a very nice current bush, which is already rewarding us with blossoms) and trying to build as much soil as possible from existing materials, instead of just buying potting soil (I may have to get a little more potting mix, but so far I've just refreshed last year's soil.) Wish me luck!