If you want heaps of coins and you've got time to spare, head through the Snow Gate to banya fields. Enter the invincibility cheat (hold down "L" button and enter A X B B Y) then find a snow man make and make him angry. Stand close enough so he stays angry and stand far enough back so that he doesnt swipe at you. He'll throw little snowmen at you repeatedly and when the little snowmen run into you they will instantly die, dropping a silver coin. You can now just leave your DS and accumulate coins automatically (make sure you leave it plugged into a power source). Happy spending!