You will need to kill the grass and weeds. The absolute cheapest way would be to spray glyphosate over the plot area (1 qt/a actual glyphosate). Get a sprayer and roundup from a local lawn & garden retailer. Gander mountain here rents out disks, I would rent that to break up the sod. Check with local lawn & garden rental companies as well, or borrow a roto tiller from someone. Buy 1 50 pound bag of winter rye from a local agricultural supplier. A 50 pound bag will plant about 3/4 acres. Buy 1 bag of 25-0-6 type lawn fertilizer for the plot. Winter rye is cheap, grows on poor soil, and you have all summer to work on your plot and gather supplies.