Home Depot, 4.50 per 1.5 cubic foot bag...Kellogg's Patio Plus...It's good stuff, just need to be cut with perlite....It's got bat guano, worm castings, kelp meal...mostly composted forest products, some peat and composted manure...pretty good stuff. Just needs extra perlite and good drainage, but it's good stuff, cheap, and widely available at HD.
By no means is this the "best" soil out there, but if you're stuck with home depot, or you're just lazy or broke, it's a good alternative. All that being said, I use it and couldn't be happier...Just needs perlite and it's good to go!