I try to get a package price I can live with. This means the vehicle and any extras or services I want. Many times, the extras will be thrown in at cost and installed for free. By adding these items, the dealer can work the numbers and hopefully come out with a price both can be happy with.
When I ordered my AF811, I configured it the way I wanted and had the dealer install vent covers on it. At the same time, they also installed the mat, tie downs, hitch, extension and y-cable I wanted.
My F250 was also a custom order. The dealer added Line-X, mud flaps and hood protector for less than I could buy them.
I progressively upgraded the wheels and suspension on my own after getting a feel for ride and actual weights.