The stuff I get is called Repti Bark from ZooMed. It can actually be screened to get a few sizes of bark out of it. I usually get about a 3:1 ratio of small bark to medium bark out of the bag. I use the small bark in mixes for seedlings and small moisture-loving plants and the medium bark in a mix for pot sizes up to about 5 inches. I've also used Zoomed's CHC and it worked well. These mixes are made to go into cages with reptiles and herps, many of which are notoriously susceptible to environmental contaminants. The reptile and herp people are just as crazy about their babies as orchid people are
I've used this stuff for at least 3 years now without any problems. The only orchids that don't go into a mix with this bark are my really big Cattleya's and Angraecum's which get a mix with Better-gro's bark (available at Lowe's) that is quite a bit larger.
Locally I can get both bark mixes for about a $1/quart. Occasionally (~2x a year) the pet store will run a buy one get one free deal on reptile bedding in which case I stock up and can get 16 quarts of bark for $8