That's a lot of hats. http://www.bit-tech.net/news/gaming/2015/01/29/steam-workshop-payouts-reach-57m/1
That's an average of $38,000 per creator. Stands to reason that some people are making an absolute killing on this.
More likely a small amount of items selling for lots and everything making next to nothing, only a few creators will be bringing the millions.