Download the mini-game "Stuff" to your VMU. 
Then, save your game. Sell everything you have 
and go to the Monster House. Buy as many tokens 
as you can. Put the tokens in your VMU. 
Reset the game and load your game file. 
You will have the money, items, and tokens. 
Next, sell the tokens and save. 
Go back to the Monster House and buy even more tokens. 
Repeat this trick as many times as desired.