This is a nice exploit, but I have improved upon it. You will need: 3 goldfish statues, and a 1 second timer, bug net (golden preferred), a rubber band or program to auto click your mouse, lots of TNT, and
tons of sand.
Now that you have your ingredients, follow this procedure to make $$$$$$.
1.) Farm goldfish for however long you can. You will need minimum 500 goldfish.
2.) Go to a desert with your TNT, and blow it up. You can do this in another map, to preserve your world's deserts.
3.) Go to your local furnace, and smelt your sand.
4.) Turn the glass into glass bottles, and fill them with water.
5.) Combine Goldfish and bottled water to get....
6.) FISHBOWLS! They sell for 20 silver each, and 500 will get you 1 shiny platinum coin. This method is more time consuming, and more labor intensive, but far more rewarding.
In just 30 minutes, I managed to earn EIGHTEEN platinum coins from farming goldfish and sand. As a result of this method, tons of mining, and over 1000 queen bee kills, I now have 142 platinum coins on a prehardmode character.
Of course you could just farm the goldfish statues, or bosses, but this method is far more rewarding, at least in prehardmode!
Hope this helps
-Techdude