The cheapest method has got to be to grow your own. The great thing is that it doesn't require you to have much garden space, or even a garden at all!
We grow tomatoes, and strawberries in containers and the extra benefit is that you get total control over the growing conditions. The best combination is to have organic soil together with organically produced seeds or plants, that way you ensure you get the full flavor and benefit. Containers can be placed anywhere that receives a reasonable amount of daylight, which means that you can use them on balconies or other hard surfaces.
We grow tomatoes, and strawberries in containers and the extra benefit is that you get total control over the growing conditions. The best combination is to have organic soil together with organically produced seeds or plants, that way you ensure you get the full flavor and benefit. Containers can be placed anywhere that receives a reasonable amount of daylight, which means that you can use them on balconies or other hard surfaces.