Think about the invoice like this...I went to Circuit City to get a computer. My receipt says $700.00, that's how much I actually spent, but with all of the rebates it comes to $399.00
The receipt price isn't true because of the rebates, but the sale price isn't true either, because you have to spend almost twice as much as the advertised price to get the 'sale price'. A really sorry way of doing business....
Without knowing all the financial back-and-forth between a dealership & a mfg, the invoice price doesn't carry a lot of meaning.
Shop around, check the net, have cash if possible, and don't be afraid to get up & walk, you'll get a good deal.