In lvl 3-2, a zombie will drop a present which will unlock the Mini-Games tab

Open the slot machine mini game
Simply play the mini game like you would normally do until you get 1975 suns.
WARNING : DO NOT TAKE ANY SUNS AFTER YOU HAVE 1975 SUNS
Leave the mini game without taking any other suns, this will create a save don't worry
Go back in the mini game and now you can take the last sun

A trophy will spawn after you get 2000 suns, do not pick it
Now quit the mini game (without taking the trophy), this will create a save before you claimed the trophy
Come back and take the trophy
You will gain 1000 coins and you will be back on the Mini-Games screen
Since there's a save before you took the trophy, you can go back in the mini game and take the trophy again and again...