You can buy one with $20 of real money and then sell it on the auction house for a starting price of 30,000 gold. After that, the price will fluctuate based on the game’s economics.
When Atlus and Spike Chunsoft got together to mash up dungeon crawler franchises Etrian Odyssey and Mystery Dungeon, the companies cleverly combined the best aspects of each series to make a crossover so well done that it should become a new franchise on its own.