It's not a Palm, but I just got my new AT&T Tilt last week and have TomTom installed on it which was a completely simple installation.
Total cost from NewEgg: $174.99 - $25 Mail-In Rebate + the costs of a MicroSD card (got a 2G Kingston for $24.99 shipped).
Set it up on the dash with a car charger and it's good to go.