I went to a local horticulture shop last night to see what they had in the way of topsoil. They did have one variety that included some compost. It was 1.70 for a 40lb bag, and that's what they recommended. Unless I decide to go somewhere that sells dirt by the yard, that's probably what I'll use. Straight topsoil was 1.40 for 40 lbs. I have no idea whether those prices are reasonable, or how far 40 lbs of dirt will go. Probably not very far.
My lawn was put in last fall, and it's been a pretty crappy year for trying to establish a new lawn, without a sprinkler system. There are a few small areas where I'm going to reseed/add some seed etc. When the lawn was put in, I purchased several extra yards of topsoil, but I really have no idea of the quality. In my opinion, there appears to be too much stone/gravel in the soil to consider it a quality planting bed. I should probably get a soil test. It's hard to find time to do all of this stuff.