There are other Keno games for the mac that cost as much as $4.99 USD. Keno for Mac from Bimza Games is Free! And while you can buy credits via in-app purchase, we also give you unlimited free credits: every time you run out, we'll give you 100 credits to get you playing again.
Get Keno version 1.2 free from the Mac App Store today and join in the world wide Keno competition. (Mac App Store Link) Keno requires Mac OS X Lion, or Mac OS X Mountain Lion.