It would be more like $2,160. Very expensive.
Yes, it's a big and expensive project... Thankfully I won't be the one paying for it

I did the math, and everything rounds out to about 9 grand... quite a handful of cash, but this is supposed to be a commercial project, so this is actually pretty cheap, compared to what a full-blown LED screen normally costs, which is in the 6 figure range...
Anyways, my plan doesn't involve multiplexing... the idea is to split the matrix into manageable 20x20 modules, each with it's own Arduino Mega as a controller, and a master controller to feed data into them (or more than one, if a single Mega can't handle the data flow)...
So in the end we're looking at 35 Arduino Mega controllers and a 36th as the Master...

Each arduino will have it's own power supply, and there will be a 12v PSU for each module, so there shouldn't be any problems with astronomical current loads and all that...
Anyways, in the end the idea is starting to sound somewhat ludicrous with all these Arduinos and whatnot... So we're now looking to other options... namely a dedicated screen controller to drive all those LEDs... I mean, if a HDTV can do it with over 2 megapixels, and refresh 60 times a second, there should be some controller out there that can do it for a 120x90 pixel screen
I'm really no expert in any of this, so I don't know much about what can be done and what can't... I'm making this up as I go along...

Thanks for all the help so far

Cheers