There is typically no fee for using mapping software with a GPS receiver - you pay for both once and off you go. Upgrades may be another matter but that is certainly not a monthly fee. There do exist some 'add-on' services (i.e. TomTom realtime traffic info) that are subscription based but you don't need them to get from point A to point B.
Arkon (
www.arkon.com) sell both GPS units and car mounts at reasonable prices. I have had very enjoyable dealings with them so far both with customer service and the products themselves.
db