Aerogels are fascinating materials, with lots of interesting and, frankly, amazing properties, but they are not easy to make. These days, industrial manufacture with an eye towards commercial applications, primarily as thermal insulators, is bringing the price down some, at least for granules, but larger pieces still cost around $50 US per cubic inch.
Ben Krasnow, impressively, has made his own, using a homemade supercritical drying apparatus. If you want to get a feel for what goes into making this material, and/or understand why it’s so expensive, and/or try to make some yourself, check out his recent post on the subject. [Thanks, Ben!]