I have discovered a trick to get money fast:

1- Enter the stage with the biggest possible price per spin (if you havent avanced a lot in the story the hardest mode of the dungeon stages have 450,000 of max price)

2- Set the price per spin to maximum (in the dungeon for example you set it at 450,000)

3- Use the abilty that grants you 5 free spins (in the symbol in the right of the eidolon)

The money you get for each spin depends of the amount you bet, so if you bet 400,000 , for each spin normally you get between 40,000 and 600,000 ,in my case i bet 600,000 and i got lucky and got the minigame so i earned 10,000,000 in a moment, and dont worry if you cant beat the stage because even if you lose you only lose the materials but not the money.

Sorry if my english is bad but i am spanish.