Audrey, I am not Barb, but this place carries Promix BX, last year it was $30 per 3.8 cu ft bale, which fluffs to about 7 cu ft. Oddly, they don't mention Promix on their website, but
I have been buying it there for years, never has been on their website.
http://universalsupplycorp.com
Audrey, here's the manufacturers page for who distributes their product.
http://www.pthorticulture.com/en/distributors/?type=pro