What if the dealer won't negotiate at all?

That's their right, and sometimes it reflects high demand or a firm pricing policy. You can ask if anything else is flexible, like removing add-ons, improving your trade-in value or including accessories, or you can walk away and compare other sellers. Get their out-the-door quote in writing so you can compare. There's no obligation to buy, and being willing to leave is one of a buyer's strongest tools.