Ni no Kuni: Wrath of the White Witch

You'll get this easily in post-game. Don't worry about saving money at all during the storyline, as you'll be dirt poor most of the time anyway. When you reach the post-game grinding, you'll get this because you'll have nothing left to buy. Farming for Super Hero alone will probably get you all 500K.

If you REALLY need money after you beat the game, go back to the final dungeon (White Castle). In the final stretch of enemies before the boss, there's a rare golden enemy named Tokotocold (looks like a little totoro with a staff) who drops 10000G if you can kill him before he runs away. He can appear with other monsters, so you can run up and down fighting them all, or run from end to end with the Veil spell until you see him.

Of course, if you're close and just want the trophy right away, you also have the option of saving your game, selling everything you own, then loading your game.