Before you make an offer, get the invoice price for that car with the options that are on it. You can get the invoice price at
www.edmunds.com
Since it's a demo, it will have an in-service date. That is the date the car was put into service by the dealership. But more importantly, that is the day the clock on the warranty started. If it was only a few weeks ago, no biggie, but if it was months ago, that is something you need to consider in the negotiations.