You can see on average I spend $290 on food per month. July, August, Sept are the harvest months where my spending crashes. I'm spending $100 less then average. That works about to about $10/hr invested in the garden. Of course the savings goes further into the year, as my freezer is loaded with food I'll be using all winter. Nicole and I canned 7 pints of tomato sauce last week, and we will be canning some more this week by my estimates. I just took some zucchini bread out of the oven and that freezes well. It makes a nice treat in mid January.
As much as I'm saving it raw currency, I'm also investing in myself. I doubt I've ever been as healthy as I am now - Nicole laughs because I don't fit into my pants anymore, and I've run out of belt loops (hard to believe I ever had to buy 34s). And that's mostly because of diet, I don't exercise anymore then one 3mi run a week and lawn care. Having a garden, with all this produce sitting on your counter, in your fridge, in your freezer, forces you to eat it. There's very little way to avoid it.
There was a recent experiment by some business students at New Mexico University which modified shopping carts by placing a line of duct tape across the middle of a shopping cart and an accompanying sign which stated "this section for fruits and vegetables." The people who used the modified cart bought 102% more fruits and veggies then those with normal carts.
Having a garden in your back yard, assuming you have the self discipline to use it, is like having a modified shopping cart. It nudges you to eat fresh, eat right, and eat locally. Next time you find yourself at the grocery store, bring the duct tape. And next spring, plant a garden.