I would say around $15,000 off MSRP would be a good deal. It depends on the rebate offer also. I bought my 2008 for $10,000 off MSRP in December of 2007. They had pretty good rebates going then. I think it was $4,500 rebate for the current year 2500's when I bought mine.
I just picked up a rare 2009 ECLB with more than $8500 in rebates. GM did not put the Duramax in the 2010 EC model and I just heard a rumor that there are no more Duramax orders on any 2010. All new diesel orders are going to be 2011. Unconfirmed but I just checked the website and can't find the option to build one.
I bought my truck in Oct. It had been on the lot since Feb 09. I bought the truck new, cheaper that I could have bought it used due to over $8K in rebates, plus employee pricing. In the end, I purchased my truck for $11k under the sticker. . Good luck and let us know how you make out.
I bought my '08 (Built 08/07/07) in April '09 for $14,000 off of sticker. Sticker was $44,410, my price was $30,300 cash, no trade. $2900 GM Card rebate came off of that. A month before that, my dad bought a new red '08 GMC 1500 ccsb 4x2 that stickered for $31000 for $17,100 cash and then got his$3500 GM Card rebate on top of that. Of course, that was when GM was at its low point, so that factors in.
There are still several new 2008 GMC CCSB 4x2 SLE2 Dmax trucks identical to mine (fleet cancellation maybe?) available. I saw them still advertised out in California and there were at least 3 in mid Missouri.
It can be interesting when a new vehicle sits so long that the factory rebates no longer apply.
Push for more. If they want the sale bad enough, they will deal. The truth is they need to move vehicles. In 12-20-2008, I walked out paying $20,000 for my 2008 CC Duramax.
$22,000 off MSRP. It was sad, they wanted $1500 more for a 2008 CC 1500 with a 5.3. then what I ended up paying.