The most expensive car in the game clocked in at 800 gold; a pack of 1,000 gold sets you back £69.99, so by our calculations the Koenigsegg Agera R is worth £55.99.
3. God mode - Super Monster Bros by Adventure Time Pocket Free ($99.99)
Tip of the hat to IGN for discovering this execrable example of the ripoff merchant's art. There are games that offer more expensive individual in-app purchases, but few can be so shameless.
Of the six playable characters, one is (or perhaps we should say 'was', since it seems - happily - to have been taken down) available for free; the others cost anywhere from $4.99 to an utterly astonishing $99.99. You get a limited number of fireball-style ranged attacks, and topping up your supply costs $0.99 a time; and when you die the game offers a sort of God mode cheat (attacks and energy are set to infinity, it seems) that'll also set you back $99.99.
Infinite jump, HP and ammo? Why yes, that sounds delightful...
*Cough* $99.99 *cough*
In gameplay terms it's total tripe, too: the most appallingly basic and derivative platform game drivel, with gaps you can't fall down, feeble effects, and visuals and sounds that seem to have been lifted wholesale from other games. Since it no longer seems to be available, enjoy the full horror in IGN's video review.
2. Apathy Bear - Gun Bros (£394)
Sometimes an app can disguise how expensive an upgrade is by charging in-app currency for it, instead of real money: hey, that's not expensive, it's only 30 Magic Coins. But if the in-app currency is itself for sale - and if the game makes it difficult to earn enough currency to pay for its best gear - then you can easily find yourself paying through the nose.
Gun Bros is a perfectly fun little multiplayer shooting game, but it's notorious for its extravagantly named and extravagantly priced weaponry upgrades. Currently the most costly piece of firepower is called the Apathy Bear ("This gun filters a child's love through a screen of inverse anti-matter sub-particles, killing your enemies with the most adorable haemorrhages imaginable"), which costs 3,999 'War Bucks'; this took top spot from the Kraken gun, a snip at 3,499 War Bucks.
To give you a feel for the prices, the game gives you 3 War Bucks to get started with.
You can earn War Bucks in-game, but it's a slow process. Or you can buy them as in-app purchases. A pack of 710 costs £69.99, making the Apathy Bear worth about £394.
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