Just confirming it's exactly like the description says, you must have 300k ON HAND, not cumulatively. I got this about half-way through chapter 5. If you're more thorough searching for chests and crystals, and don't spend as much as me, you can probably get it in chapter 4.
Do note there is a finite amount of enemies, chests and crystals in this game, so it's possible to spend so much gold that this is no longer obtainable. It isn't a Diablo game where enemies always respawn.