A good book on seed saving.
In the grocery market one small pint of cherry tomatoes cost $2. Leaf lettuce runs around two dollars a pound. Much much cheaper to grow your own. Two vegetables that are cheaper in stores are carrots and potatoes. I am hard pressed to think of other vegetables that can be purchased cheaper than I can grow. A dozen ears of corn cost about $2., that is just six corn plants, I can get a thousand corn seeds for ten dollars. I do buy avocados because I cannot grow them in my area.
One small 12 oz can of diced tomatoes cost a dollar in the markets. Canning your own food is allot cheaper. I have a freezer full of corn and green beans. What I do not preserve makes great compost.
The number one cost in home gardening is your personal labor cost which I did not include. That personal labor cost is the factor that determines if gardening is profitable. Eight hours of fishing might bring $20 worth of fish, for some personal cost is important, some it is not.