Please explain how one accurately obtains both "invoice" and "holdback" figures as I don't imagine dealers are forthcoming with this information.
Invoices can be found from AutoBytel.com, and many other outlets. But Invoice does not mean the price the dealer ends up paying for the car, or making on the car is more accurate...
The holdback can be a % of the sale price, or a set figure, $650, etc...
You can often find holdback numbers online, and Automotive News is an inside the beltway (pay to play) dealer publication which provides just about every scrap of information.
Holdback, you won't likely ever get.
IMHO, the dealers you want to work with are those that are going after incentive programs by the car makers themselves. Thus, find a high-volume Kia dealer (the larger the odds are they play the volume incentive game with the factory), then mid-late month, if the dealer is tracking to get over their target sales figure (say, 120 cars), they will often sell at cost, and in some cases sell at losses.
Automotive week had a dealer talk about selling cars at a loss if they an make their incentive sales figure, but it is risky. Miss the target by one car and they get nothing - and sold some cars at break even or losses to make matters worse.
However, if the dealer hits their sales incentive figures, presto, they get a nice big check from the auto maker.
Just talk to some of the lower-end sales guys on the lots or talk to service folks, or a fleet manager, you'll get an idea pretty easily if they a volume loss leader dealership or not.