2000 Ford Taurus actual cash value of vehicle

My 2000 Taurus SE wagon was hit and the other persons insurance company wants to total the vehicle. They claim that $4950. Repersents 105% of actual cash value. This wagon was in excellent condition with every option except cd player and moonroof and only 54000 miles. I paid $6500. 18 months ago from a relative. How is actual cash value determined? And should I accepept the insurance companies offer or can I negotiate a higher price. What other resources are there to help me arrive at the ACV for this car?"

Thanks for any help.

Randy