You don't need the VIN to find out the dealer invoice price on a car. Just click on the New Cars tab above and Edmunds will tell you what the invoice price is (and MSRP and what the True Market Value is).
Note that dealer invoice is not the same as dealer cost. The manufacturer may give the dealer incentives, rebates, free advertising or spiffs that lower the invoice cost.
Edmunds will tell you if there are any manufacturer to dealer incentives (marketing support) in your area, but only the dealer knows what the actual cost of the car is.