Guess who dropped 500 k on the X-Factor Finalist

You know you're rich when ... you spend $500,000 to upgrade 160 "X Factor" contestants to a "nicer" hotel simply because you felt like it -- like Simon Cowell just did.

It all went down in Miami ... where the 160 wannabes who made it past the audition rounds are competing for 32 coveted spots. 

Sources tell us ... Cowell -- who created the show -- decided he wanted to reward the contestants for making it this far ... and didn't want them slumming in a "regular" hotel. 

So he upgraded ALL of the contestants to the exclusive Mondrian Miami South Beach Hotel ... and promised to cover everyone's meals during the audition process

We're told Simon's expecting the total bill to run somewhere in the $500k range ... which would probably sting ... if he wasn't a gazillionaire