I buy bales of coastal hay for about $10 a bale and spread it around (I also use this for cushioning in the dog houses). You could probably buy a few bales and take care of your entire garden, but start with one or two and see how far they go.

I found bagged decomposed granite at Home Depot last weekend, and today I opened it up to take a look at it. (About 40 pounds, measured it is .5 cubic foot of crushed stone, cost about $4.50) My organic guru recommends it as part of the mix when you're making potting soil or improving the garden soil. I sprinkled it around my gardens sparsely, just to get the feel for handling it, and this will work it's way down through the mulch during the season. I regularly use lava sand and green sand as amendments. This is a little different, it is for consistency, not minerals, as far as I know.

SRS