here is what I use for coco

11 lb for a little over $2 a pound

Edit: although I realize it might not be economical for a lot of people, a reciprocating saw will definitely be your best friend.

I like these for my microgreens. I rinse them in a tote before adding ocean solution. A little more labor intensive than buying bagged loose Coco like your craigslist guy, but super cheap and works very well. And none of the useless perlite in it. All perlite will do for microgreens is cause the medium to dry out faster.