Perlite was pretty cheap when I bought it in a large bag from a building materials place, far, FAR cheaper than a nursery. The bag was about 36" tall x 18" wide or so. I use it for concrete and planting. At some places, it comes in different sizes.

Check and see if you have a Mutual Materials around you. They're mainly a wholesaler, but the one here has absolutely no problem selling retail.

Sue