The 2/3rds mentioned above is in the ball park if based on retail, but not on street price. Typically, most dealers get a "B mark" cost on products like the Electribe and other synths. B mark means 40% off retail. An Electribe EMX-1 RETAILS for $750. Retail x .6 = $450. Street price is $499 so a typical dealer makes about fifty bucks (10% GP) on it. Guitar Center adds 12% to the cost at the store level, but they also get a better deal from Korg for the qty's they buy so it works out about the same. But to say that any store pays $330 for a unit that streets for $500 and makes $170 profit is just not accurate. This is why when you receive a coupon from GC for 10% off your next purchase of $299 (or whatever) it always says it's not good for Korg, Roland and most of those "B mark" brands because 10% is about all they make on it.
GC also hides their actual purchase price for their gear from their sales people as well(According to a friend of mine who is a store manager).
So what they say is their cost is in their computers is actually higher than the real cost. Apparently to keep a profit margin.
The way I always buy from GC is to find the best price I can online and bring in a printed version of it and show them. They have to match the price plus take another 10% off of the difference no arguments, doesn't matter what brand. I save a lot doing it that way.