Dealer cost is difficult to find. Go in the other direction and take 20% off of the MSRP. Doesn't matter much.
I'll use this
Crownline as an example.
MSRP is 45K. First you must know if this is the rig you REALLY want. If it is be prepared to buy it. Have your financing lined up or at least know what payment X dollars is. Never, NEVER switch to payment negotiations! As a salesperson I'll kill you on payments. Know in advance the MOST you are prepared to pay for that rig.
Note the asterist** *
Price, if shown, does not include government fees, taxes, dealer vehicle freight/preparation, dealer document preparation charges or any finance charges (if applicable). Final actual sales price will vary depending on options or accessories selected.
Find out about prep charges and any other fees beforehand and have the salesperson show you how much this 45K rig will be 'out the door'. You'll probably have $3K in sales tax, maybe more. Title fees, doc fees, prep fees and your at $50K before you know it.
Now the fun begins. Everything is negotiable except taxes and state titling fees, most certainly the 'prep' charges. Work backwards from the 'out the door' price. Pull out a nice wad of cash and tell the nice salesperson you'll buy that Crownline today for ???? 40K? 38K? Whatever. You won't hurt his feelings.