At the end of the game, before you battle the Chaos Chimera, walk around the Apollo Sanctum to get into random battles with the Tua Warriors. It is recommended that you have one of your party members, that is not in your "battle party" equip the Lure Cap. They will almost always drop Water of Lifes. You can sell them for 2250 coins. Thirty of them equals up to 67,500 coins. 240 of them would equal up to 540,000 coins.