When thinking about the term "overpriced," you need to look at the competition. I had been using a Belkin Auto Kit that cost me around $60 with my 3G and 5G iPods. Unfortunately, because of the way that Apple reconfigured the dock connector, it won't charge any of the new iPods or iPhones. I was considering replacing it with another Belkin - the TuneBase Direct or the TuneFlex. The former is similar to the TomTom offering, but doesn't have a GPS antenna and appears to use the headphone port rather than the dock for a line out (except I see what looks like a line out port on the side of the plug, so I'm not sure).
It's $70.
Don't be surprised if it retails for $100/$70. I certainly think that would be a fair price in comparison, and would tempt me to go with a straight TomTom solution rather than Navigon/TomTom.