2 cu. ft. bag of Grodan Mini-Cubes is about $35 at my local hydroponics store. They also carry the chunks. It's my go to source for fertilizers, coarse perlite, and pots. For some reason, the prices are much better than at two other hydroponic stores in my area. I'm not complaining
Live sphagnum moss from neighboring pots became established on the surface of Phrag. longifolium and sargentianum. I've kept a close eye on it, and both plants are doing fine. I'm not sure if it's of any benefit, but it is supposed to have some antibiotic properties.