Yeah, I wouldn't get an in-dash one. Updating the maps will be very expensive (on my dad's 2005 GS430, they were asking $250, not including labor) compared to mounted units. And, also, there's more convenience and flexibility with a mounted GPS. Updating the maps usually just requires purchasing a disc. The unit can also be used in other vehicles and even while walking.
You can wait until the end of September or beginning of October when Garmin usually releases their new models. Their older models will go on big discount. I'm sure the same goes for the other brands like Magellan, TomTom, etc.
I like the Garmin brand and have a Nuvi 660. 2 years and no problems.
And, there is always Black Friday!