[fritz_t_coyote]

An aftermarket GPS (Garmin, etc) will run you about 300$ or so at Staples. You can probably find a good deal if you shop around.

I bet the Dealer version costs a lot more.

Save your money... A GPS is only as good as its map set, and unless you can update the maps it will be annoyingly obsolete in a few years. Some GPS's let you attach them to a computer to install new maps (which you may have to buy every year or two, but it beats replacing the whole GPS).

Other must-haves: Voice directions. Repeat Button. Common Sense.

Happily since PT's do not ship with metalized windshields, a GPS on the dashboard can get a good view of the sky, no additional antenna is needed.

(Common Sense is critical when using a GPS. I once had a GPS tell me to drive the wrong way down a one-way street in front of a Police Station. What was worse was this early unit (an add-on to a notebook computer) sounded just like Stephen Hawking; it was not easy to ignore directions from the smartest man on the planet.)