Whoever coined the phrase "dirt cheap" never gardened in raised beds.
While I budgeted for lumber, screws, and seeds, I didn't factor the cost of so much soil.
The official Square Foot Gardening additives--peat moss and vermiculite--would require a trip to a nursery and the purchase of additional compost.
I found a frugal alternative in Lasagna Gardening. Starting from the grass up, we layered newspaper, chopped dried leaves, peat moss, grass clippings, and compost. Over time, this will break down into prime, rich soil.
To compensate for this year's oops, we added an additional layer of Miracle Gro Organic Soil (a Big Lots bargain at 2 cubic yards for $8). If we had a truck, we could have picked up the city's compost for much less.
Mother Earth News' handy conversion chart helps you compare bulk vs. bagged prices.