As Skata says you get a bigger bang for your buc with an after market unit like my Garmin Nuvi 660 for $800 shown here in my old Maxima.
It came with a mounting plate for dash or windshield, I went for the bean bag option because when I leave the car there is no tell tale marks on the windshield or a plate to alert a thief to it's presence. The 660 is thin enough to fit in a shirt pocket and the bean bag is left of the floor.
First you see it
Now you don't

Great little unit, talks to me, finds me shopping, fuel, restaurants, takes an SD card which is great for audio books on those long trips etc