Hey plusminus.
I think it's ok to sell a navigation system for ~20$.
But there is a problem:
When the user spents money, he wants to get a
working navigation system. Not one which has corrupted map data. I think there would be a lot of dissatisfied people if you sell such a system.
Also, the spreading of a payed-application will not get too big compared to a free application. And you need a big spreading for supporting OSM.
So why selling the application? In Web3.0

there are other revenue models!
Such a navigation system, with all-time internet access, is predestinated for location based advertisment.
Think about a navigation system that recognizes, that you drive in a new city at 10PM. It knows that you drove 6 hours so far and so it displays you the next Hotel! Or a good restaurant! Or that walmart sells the G1 for 10$..
This is the next level of advertisment - this is why google develops Android.
Greetings,
Michael the
Androidianer 