This trophy can be earned quite quickly, even in the first level! Throughout the first level there are many treasure chests scattered about. Find each one and open them. Some will give you a bag of money for 100 in currency. Others will give you a few coins, each worth 10 in currency. Killing enemies will usually only give one coin. Once you have collected all (or most of) the treasure chests, you may die without beating the level and begin again, as the treasure chests and enemies should all respawn.
The video below by KingSuperOne illustrates this.