Let me expand on my earlier post. Use of the GPS signals from the satellite constellation is free. When you buy a GPS receiver, it comes with a basic mapset...over time, the software gets updated as new roads are built, new businesses are developed, etc, and if you want the very latest information you will probably have to buy updated software from the map data provider...but this is not a subscription or monthly fee. You can use the original mapset forever if you don't care about updated information.
My StreetPilot III came with major freeways and cities in its memory. In order to get down to street-level accuracy I had to buy additional software, which is frequently updated by Garmin and/or MapSource. These online updates are free, but if I want to update the basic mapset it is going to cost me.
In the aviation world, GPS receivers contain databases with info on airways, navigational waypoints, airport data, etc etc and the FAA requires that a current database be installed in order for the GPS to be used to fly under instrument flight rules. These database updates are not cheap. Still, pilots use the signals received from the satellites without charge.
Bob Gardner