On a recent morning, thinking I might be able to catch a performance of Porgy and Bess at Lyric Opera, I checked Lyric’s website. The cheapest seat in the house—a perch in the vertiginous reaches of the upper balcony—would set me back $59.

And you don’t have to pretend to be a kid or a college student to claim them. (Lyric has had discount programs for them for awhile.) You can just walk up or go to the website, and take your chance at getting lucky. It’s like playing a very little Lotto, with way better odds.

That means, unless you’re buying season tickets, prices, especially on the upper end, are in flux. Advertising will generally indicate only something like a “tickets starting at” figure.

The last time I looked at the Goodman website, a main-floor ticket to see Larry Yando’s dynamic turn as Scrooge in A Christmas Carol would cost you $101 for a Sunday matinee on December 14 and $83 for an evening performance that Wednesday. And Lyric was offering a $99 special on all remaining main-floor tickets for Porgy and Bess.