I purchased a 2012 Mazda3 iTouring in August 2012, for $18,667 otd. And the dealership installed aftermarket heated seats ($500 value) at no charge.
I believe the pearl white paint has an extra cost.
My car is a manual. The auto trans adds roughly $1000
Mine's also a 4-door. The 5th door adds about $600 to the base cost.
$20,100 sounds very reasonable for your car. Did you buy it? Have you had it for nine months now?