I heard the Little Big Planet series is quite bad as well with those costumes...

DOA 5 is the worst I've laid eyes on. Mental. But there appears to be worse on PC.

From what I've heard, some of the most ridiculous amounts of paid DLC actually show up in "Fee to Pay" games, as Jim Sterling likes to call them. Games where a significant chunk of the game is hidden behind paywalls for no other reason than the developer/publisher wants more money (and usually it's stuff that, in the past, has been included in the base game). Don't know if they're especially ridiculous in terms of amount of money you have to spend, but it's ridiculous anyway.

Here's an article on some of the worst cases of DLC, though: http://www.gizmodo.co.uk/2015/04/the-most-obscenely-expensive-gaming-dlc-ever/ - Train Simulator is on there, but it's not the worst. I'm pretty sure having an in-game item cost £34,000 (that's in real money) is much worse than having a lot of little in-game items costing $3000 combined.

It's worth also noting that Hyrule Warriors and Hyrule Warriors Legends competes well with this.

For US$20, you get two completely new characters (Tingle and Young Link), one kinda-new character (true form Midna), 5 new story mode scenarios, three new adventure mode maps, the Epona weapon for Link, the Copy Rod weapon for Zelda, a heap of new costumes, and two new game modes.

Note that much of the content of the game is in adventure mode maps - so US$20 pretty much triples the amount of content in the game.

If you get Hyrule Warriors Legends instead, you'll get all of the above for free, and then get more - five more characters, a new weapon for Ganondorf, new features, new story mode scenarios, new stages, etc.

Then, for HWL, another US$15 will get you four more adventure mode maps, four more playable characters, new weapons for Linkle and Toon Link, and more options for one of the new features. And if you have both games, you'll have a download code to transfer the HWL characters to the Wii U version, and another US$5 will let you get the other new characters and weapons for Wii U as well.

Oh, and they've also released three freebie DLC characters (Cia, Wizzro, and Volga), and they'll be releasing another one (Medli) soon.

Not nearly as much as those games above, but the most I have spent on a game for DLC is Europa Universalis 4. I have spent easily over 100 on DLC for that. But it is worth it too me. I have played it for 700+ hours and each 15-20 dollar expansion pack gets me back into the game gives me another 50-100 hours.