Thanks Bill for the plug
Justin, the mix I sell is more expensive at first glance. There is a reason for that. Its got more in it than turface, sand, and bark. Its comprised of Akadama, lava rock, grani grit, New Zealand white sphagnum, turface, and a variety of micro nutrients. All ratio'd from Colin Lewis's Recipes. You also get a 9 pound bag verses a 2 pound cited in your link. So your actually getting more for less. The mix is dynamite anyone that has used it has raved about it. There are three mixes Conifer, Deciduous, and a special mix for pines. Here is a pretty good
article Colin wrote about soils.
Good luck in the soil hunt