When Dr Johnson described opera as "an irrational and exotic entertainment" he implied something else: opera is also vastly expensive. Nowadays it may be a touch less irrational, and isn’t always set on a magic island or in a Duke’s castle. Even so, it’s still expensive, and that means that in straitened and somewhat puritanical times opera, more than any other artistic form, is vulnerable to cutbacks. Some months ago New York City Opera collapsed, though it went down fighting by offering Mark-Anthony Turnage’s Anna Nicole as its final production, rather than a crowd-pleaser. Some weeks ago San Diego Opera threw in the towel and announced that it was going into voluntary liquidation, though it seems that decision is now on hold.