That's the ballpark figure that I got when inquiring at my Washingotn dealer for the 3rd gen SC.
If you don't mind the extra cost, that would be a good way to go, in my opinion. If you are leasing, the last thing you want is to pay extra for "unwarranty'd damage."
My other recommendation is to part it out upon lease termination. In this case, have your buddies remove the part and then ebay that bad boy. I'm certain that the open market will give you a better price than the dealership -- unless you can negotiate that into bringing down the price of your next vehicle
If the dealer takes it off your hands to resell, the whole idea is to pay you LESS than what they think/know they can resell it for. You may as well cut out the middleman -- seeing that ebay is a great marketplace, as is this site.
If you do go with the Supercharger, please remember to carry a camera with you at all times. I would ask that you take and post a photo of the first time you leave a BMW M3 in your taillights on the freeway... 335 ponies..339 torque! The M3 will probably out-do you in the turns... but he'll have to catch you first.