I really have no idea what you mean by a DCM upper. Its a standard post-ban A2 upper. The only difference I can tell between it and any other 20" A2 Upper is that the barrel is stainless steel.
Here is the exact item I am selling on the Bushmaster website:
It sells new for $585.00 and mine is used but in extremely good shape (about 100 rounds through it).
In fact, for cash buyers, I am even willing to throw in the scope and mounting rail I have attached to the upper. Its an NcStar scope (I know, not the best) but its a rather neat setup because I have it setup so that I am able to use both the scope and the iron sights without a problem.
I have ZERO complaints about the accuracy of this upper, I have just decided that a carbine fits my purposes better than a full length rifle.
Just so people are clear: if you are willing to trade uppers I am looking specifically for uppers built by a highly reputable manufacturer (Colt, Armalite, Bushmaster) that has a 16" barrel, pre-ban configuration, and chrome lined chamber and bore. I don't like the "ultra-light" models - I like a heavier barrel. I need an upper WITH a bolt and charging handle assembly because I am selling my bolt and charging handle with my upper.