As a former Parts Manager, and one that worked for a couple of dealers ([X(]) I can tell you that that is likely to be the best your gonna do too. Dealer Parts counters don't usually work on much mark up and it sucks!!
When I worked for Jeep, my mark up was usually less than 20%. It was hard to entice new bodyshop business in when I could only offer them a 10-15% discount over regular retail... believe me!!

 

I realize this is an older post, after searching I found this and figured it was best to ask here. My 08 currently has the wing spoiler and I would like to get that changed to the lip spoiler. Since the wing is screwed on and the lip one is secured on with an adhesive, what kind of work would it be to make the change from wing to lip?

 

Clearly, a bunch of bodywork, or a trunk lid in your color from a wreck would be your only viable options.
Much easier going the other way, which is what most people want.