Bonsai soil and Pre-bonsai soil

[Brain Treez]

Here I can find it for about 100-125USD per cubic yard (so about 50-65 cents per gallon).

Just chiming in with another data point from Oregon. Pumice can be had for ~$55 a yard, or if you don't want so much at a time, $6 for a 5-gallon bucket. I don't have anywhere to dump a yard of rock, so it's by the bucket for me.

I use majority or full pumice for all my early development trees.