I know that at some point I saw someone mention (I think it was here at DG, but I can't find it) that you can get perlite much cheaper at home supply places if you search outside the garden section because it's sold for some homebuilding purpose. (Sort of like how epsom is much cheaper if you don't get it at a garden store.) Anyone know what it's called (if under a different name) and what section it's in? Hints appreciated. Thanks.
If you don't need huge amounts, I get mine at The Big Orange Box store in 3.9 cu ft bags for around 19.00 ( I think...it's been a while) it was a local product from here in AZ. You can also try masonry supply places. they sometimes sell it as light weight aggragate for plastering.
The product is perlite not be confused with vermiculite, and is sold here under the name of ThermoRock. it looks like white shredded styrofoam. It comes in a large green bag and I found it in the garden section. Word of caution: Always wear a dust mask and safety goggles when working with this stuff. It is basically puffed volcanic glass and can do nasty things over time when inhaled.