Ask the dealer Sarah!
Start by saying how much for cash?
Then tell them you can get a better deal else where. Refuse to name other dealer, or disclose the price.
Tell them you'll buy now if the price is right.
Then comes the difficult bit. You must judge when you think you've beaten them down enough. It depends on the make and car but you should get 5%+ off. Perhaps more for certain less popular brands.
When you've reached the rock bottom price, ask about what they can include to sweeten the deal. Mats, mud flaps, stereo upgrade - whatever is available.
One last tip. Buying now or Feb. is when dealers are busiest. 25% of their new car sales will be Jan, with 50% of their new car business will be done before the end of March. This is critical. Ideally buy in mid March as they will have their eyes on volume rebates and discounts, and will be quieter. Do not go in to do a deal at the weekend either. Go in early morning during the week.
I hope this helps.