expired GTA: Vice City for Mac $5.49
This was posted 1 year 1 day ago, and might be an out-dated deal
Feeling nostalgic for some people-wacking, car jacking, time wasting? Rockstar's got you covered.
Mac App Store download, lowest price since August 25 '11. (http://appshopper.com/mac/games/grand-theft-auto-vice-city)
Currently at a lower price than steam ($9.99) but not cheaper than steam's sale price ($2-ish IIRC, plus steam is for both mac and windows)
I do realise this isn't really 'the cheapest ever' but for a MAS release, it's a pretty decent price. Plus there's all these iTunes deals going around so. :)