Microtransactions aren't a new trend by any means, but they generally stay within a reasonable price range. It also helps that most of these games allow players to earn ingame currency by playing, albeit at a greatly reduced rate.
In the case of Glu Mobile's twin-stick shooter Gun Bros, that "reasonable price range" has taken a bit of a jolt. The game's top weapon, The Kraken, has received a price increase that sets it at 3,499 Warbucks (Gun Bros. ingame currency); that roughly translates to $500 if you were to buy the gun outright.
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Having played Gun Bros (but only a little bit) I can say that earning 3,499 Warbucks is something that wouldn't be worth the time and effort, though it is fairly enjoyable. It's a disturbing trend, but the worst part may be that people actually pony up to win the game. I may be alone in this, but playing the game is at least half the fun.