FFX: It's All About the Money Achievement in Final Fantasy X / X-2 HD Remaster
FFX: It's All About the Money10
How to unlock FFX: It's All About the Money
After leaving the calm lands, you will cross a bridge on your way to Mount Gagazet. An optional path under the bridge will lead to the cave where Yojimbo waits. Defeat him to recruit him as a summon. See here for more info on this battle.
Note: When you recruit him, always select the third option when he asks how you'll use his power ("To defeat the most powerful of enemies") and then try to negotiate his price. You'll need at least 190,350 gil on hand to recruit him with the best possible negotiation.