Have you ever visited http://www.openstreetmap.org/?
OpenStreetMap, in case you don’t know, is a sort of Wikipedia for maps, contributed to by all, owned by all.
OpenStreetMap creates and provides free geographic data such as street maps to anyone who wants them. The project was started because most maps you think of as free actually have legal or technical restrictions on their use, holding back people from using them in creative, productive, or unexpected ways.
The OSM maps are exportable to Garmin GPS devices.
I did it myself on my Garmin 76CSx. Find the script I wrote here.