There's also a few other titles (which appear to be just placeholders, not official Apple software, unless they're going to premiere some new apps with the App Store) at various prices. There's a dice game called Roll 'Em which is priced for free, an app called Color Studio at $29.99, and another game called Fast Lane priced at just $4.99. So as you might expect, there will be prices all over the place. Just like the iOS App Store, developers will probably come up with all sorts of ways to fund and profit from their apps, so I'm sure we'll see some popular free games as well as premium specialized apps.
But it sounds like Apple is aiming to hit about $15-20 for a standard full-featured Mac app. The question, then, will be what customers are willing to pay -- obviously each app is different, and each customer has their own priorities, but it'll be very interesting to see, as the Mac App Store debuts, just what happens to prices on this software.