The value of money in that game is as abysmal as the value of yen in RL. Yen you can somewhat understand since Japan doesn't have a lower denomination currency at all (like dollars/euros have cents), it's just the yen and yen only, so you need to be able to price anything from a single lollipop to a cruise ship in yens. But the currency in this game is supposed to be gold. If everything costs so much gold, it means gold, as a metal, is super common in that world. In real history gold was used as the material for the most valuable coins because it's rare. Silver wasn't as rare, so silver coins weren't worth as much. However, in that game 1 million gold coins isn't really that much, in the grand scheme of things. However, just how much gold is a million coins? It would be enough to give the house gold plating.
In the end it all boils down to the author wanting to use a currency that's worth as little as yen for convenience, but still wanting to call it gold, because it's a fantasy setting, not understanding it doesn't work that way.