The price of law school casebooks (as well as college textbooks generally) seems to grow every year. At the present time, many casebooks cost over $200 when purchased new. The high cost is made worse by the appearance of a new edition every few years, which makes the cheaper used books in short supply (or completely unavailable). New editions seem to appear every five years or so for many casebooks, and this is true not only in fast-moving areas of law, but even in subjects where most of the cases are decades (or centuries) old.
We as faculty can greatly reduce the cost of casebooks to students by simply opting out of new editions and staying with the older edition. This makes more used copies available, lowering the cost for students, and reduces the burden on us of updating reading assignment page references to substantially the same material. Although the publisher may not directly sell new copies of the older edition, there are ample sources available from third parties, both new and used. Indeed, upon the appearance of a new edition, there is often a glut of new and used books that hits the market for low prices as the old edition becomes obsolete. These can be acquired for pennies on the dollar, saving students significant amounts of money.
I adopted this strategy for the first time this year, buying up used casebooks for my Pepperdine 1L students from Amazon and other websites (see below). These used books were available at approximately a 97% discount to the price of a new copy of the new edition. This saved my students over $11,000 and probably saved some trees as well. I doubt that the students will miss out on any great new cases by using the earlier edition, and to the extent there are new developments I can supplement the readings myself.

One of the things I like the most about this approach is that it works best when new editions of a casebook appear very rapidly. The publishers that create new editions every few years will have older editions that are less out of date, making them easier to stay with. The publishers who update only when new developments warrant an update will make it harder to use older editions.
Of course, this strategy does not work for all areas of law. I doubt I would assign a casebook on healthcare law or Internet law, for example, from ten years ago. But most of the first-year curriculum changes only glacially, and with just a few supplemental cases the students can be completely up to date. I hope that more faculty will adopt this strategy, at least until the day when there are good open source alternatives for casebooks.