I had another though, for this one you will need some tools.
You will need:
1 Bunny
1 Box
1 Sharpie marker.
Put the bunny in the box, and use the sharpie to write the word "bunny" on the outside of the box. This is just a friendly reminder incase you forget whats in that box thats sitting on your passenger seat as u drive to the dealer.
When you go into the showroom bring the box with the bunny in it with you. If the dealer makes you an offer you like, go for it. If he doesn't its time to use the tools you brought with you.
What yer gonna want to do it open the box and grab the bunny by its ears. Pull it out and hold it up so everyone in the show room can see. Next you are going to want to reach your hand behind your back and grab the gun that is tucked in the back of your pants. Pull the gun out, its important to make sure there are bullets in it.
Now the next part is important. Put the gun to the bunny's head, and start yelling. I mean you really need to yell. Shout things like "If you don't sell me that car for X dollars right now this f-ing bunny is going to get his f-ing brains blown all over this show room"! It is very important that swear. A lot. It also helps if there are children watching. Shake the bunny viciously at them and ask them if they like bunny stew. Fire a shot or two into the air to let them know you mean business.
If anyone approaches you pistol-whip their ass into submission while screaming at them "why do you f-ing want me to kill this poor f-ing bunny!? do you f-ing want me to kill him!? why the F would you want that? if this bunny dies its your f-ing fault!!"
You may need to improvise a bit here and there, but the general idea is; If you don't get the price you want, murder the damn bunny. Just keep re-asserting that fact and eventually they will come around.
Anyhow, yeah that should work.