To get real easy money, buy the lure rod. Then buy two of any lure. Equip one lure to the lure rod after you equip the lure rod. Go to the lure rod status screen. Now keep adding the same lure over and over again. You can get up to 998 lures on the rod before it will reset back to one. Be careful: If you equip the lure when you can see what lure is on the rod, it will automatically reset.