I would go under 20k personally, you can always come up with your price when they counter but it is much harder to bring your offer lower. Ask for $18k since they are likely to be highly motived in terms of moving the car off the lot. Car sales have been very slow so you will be surprised at how much dealers are willing to take off list prices just to get rid of inventory. Plus, it is a demo and that is also a big bargaining chip for you.
Good luck and welcome to TSL!
Good luck and welcome to TSL!