When I was at Lowe's the other day picking up "garden soil," I noticed their 25 quart bags of Miracle Gro Potting Mix (regular, not moisture control) were on sale for $5 each. By my calculation, 25 quarts is about 0.8 cubic feet, so eight and a half of these bags ($42.50) would be about the equivalent of a bag of Pro Mix (6.8 cubit feet, uncompressed). I'll pay a little extra to get it in smaller bags so I don't have to shove a compressed bale around.
Lowe's Memorial Day prices go through tomorrow (Wednesday, 5/30).
Oh, and I'm using the garden soil so I don't have to dig to plant irises. I like to plant irises on a mound.. so I'm just going to pour some dirt from the bag on top of the existing soil, then shove the irises into it.