If you are buying straight from the plant, then you have a little more leeway. Many dealers get what is called holdback. It's money that a dealer gets from a manufacturer automatically. The longer the dealer has the car on the lot, the less money they make off of the hold back because the dealer is paying interest on that car.
Most holdbacks are around 2%-5% of the vehicles invoice. It works out to be anywhere from $300-$1000. If a dealer orders a car straight from the manufacturer, that's straight profit ON TOP of what they make over invoice. The dealer doesn't have to pay any money in interest for keeping that car on the lot.
But, if a car has been on the lot for say 6 months or longer, that car is starting to cost them money. They have to pay on interest for having that car. The longer they sit on it, the more it eats away at their profit.
What this means to you is this - if you order straight from the plant, you can make an offer right at the invoice price. Assuming that this particular car manufacturer does holdbacks(some do not), the dealer is guaranteed money reguardless of how close to invoice that you are paying.
You need to watch out. Dealers will try to tell you that holdbacks are deficeits to them. They are not. They are only a "loss" if the car has been sitting on a lot for a while. They'll try and stick you with that costs....if they do walk out. It's not your problem that car hasn't sold. You shouldn't have to pay for their lack of business.
Head over to Edmunds.com. They explain it pretty well. Edmunds also shows you what particular models/vehicles are going for, and what is a reasonable offer to make on a car.
The biggest thing to look into though is financing.
Skoorb, will you be financing, or will you be outright purchasing? You really should make your purchase based upon what financing you can get. $200 difference on the price of the car between two different dealers is trivial if you have a .5%-1.5% difference in interest rates between two different places. That 1.5% could be upwards of $1000 dollars of difference over the course of the loan. Definitely do the math on the loan before agreeing.