something very similar you may look into are gambling machines.
often they can have decent sized arrays of smd rgb led's
here is something i came across
http://tinyurl.com/2x7u7y
as for do these things really cost thousands, i think the answer is yes .. easily.
commercial electronics in general are very pricey especially things that aren't mass produced. you would be amazed how much things can cost.
in the above gambling machine example, this is an array that is much smaller than what you are proposing and the seller states that the panel itself cost thousands of dollars originally.
this is interesting:
http://www.ledtronics.com/ds/rgb1004/