Also there are those coco bricks you can buy in pet shops, they are cheap but you have to prepare them by soaking and what not.
Also a heck lot of flushing to remove all the salts they contain. Unfortunately the blocks tend to be made of the lowest quality materials, not much use for growing weed. That said, they can be very economical if you are willing to spend the time to flush all of the salts out. Coco is great since it starts as a nutrient free medium. 100% clean