I just got this myself after years of TG ownership. Great game. Why the enormous markup on them? I realize the game was towards the end of the TG life-cycle, but it's going for a rather large amount. I picked up a decent Turboexpress that happened to come with this game, sold the TE for more than I paid for both and kept the game. 
Air Zonk is fairly sought after by Turbochip standards and is one of the later titles that doesn't have a hard case. Because the hard case-less games are harder to find completely complete, collectors pay a premium for them as such. Because a majority of Turbo collectors are idiots who don't understand collecting, they still charge and often pay a premium for the much more common loose copies. Since loose copies started advertising for more, misguided "collectors" started charging more for completely complete copies, because logically they are much more valuable, being that much rarer.
It's all part of the anti-logic that has unfortunately spun the Turbo market out of control.
