Wow, lots of great comments about alternative ingredients in CP potting mixes (fired, puffed clay (Aliflor among other names), lava rock, diatomite (Dyna Rok II)), etc.
Thanks everyone for the comments and contributing to the discussion. I am not a fan of perlite because of its stark white appearance, its tendency to float and rise to the surface of the mix and overflow the pot, and its "dustiness," although it can be rinsed before using. I may buy a small bag of each of these other ingredients to try. I prefer something that weighs a little more than perlite but not necessarily as much as silica sand, because I use urethane foam pots and need something a little heavier to help anchor them.
One of the reasons I was interested in these ingredients is because the only source of silica sand I have in my region (that I know of) is a home/construction store that sells blasting sand. But the price of a 50 or 100 lb. bag just doubled within the last several months, to about $15 (50 lb.) and $30 (100 lb.) per bag.
I know that the other amendments mentioned, the expanded fired clay pellets (which I am very interested in), the mined diatomaceous rock and porous lava rock, may not be much cheaper, but they have the advantage of also providing aeration and water-retention capabilities.
I believe, from my own family's experience owning a small pottery, that the expanded clay, having been fired and therefore fused, will likely not shed too many minerals into the water and potting mix, so that will keep the TDS (total dissolved solids) down to an acceptable level. I'm more afraid of the diatomaceous rock, fearing that although it is about 90% silica, the other 10% of various minerals might be water soluble, even if slowly, and may burn the roots of some carnivorous plants. (Anyone have any comments about that?). With the lava rock I have a similar concern. Although the rock is fused and almost like glass, it may have lots of other minerals other than silica. I'm wondering how fast they dissolve in typical CP acid soil and whether they overload the potting mix and water with those minerals. It is for this same reason that I avoid gravel with its usual varied mix of types of rock. Crushed quartz may be an exception, since it would be almost pure silica.
Perhaps these fears (about minerals from these additives being dissolved at to rapid a rate in the water and acid soil) are exagerrated however.
I have enjoyed reading the discussion. Thanks everyone--
Steve / xscd