Following a comment today, and further investigation when I got home, I’m going to retract what I said about the free Garmin World Wide Basemap, at least for the 60CSx. The transfer to my unit appears to have not worked, and I now believe that what I am seeing on the screen is nothing more than the 60CSx’s built-in Americas autoroute basemap.
I have no reason to believe that it would not work in a nuvi, and I have to wonder if it wouldn’t work for any Garmin mapping GPS, if you ran it through MapSource, which requires significant effort. We’re talking registry hacks or the use of GPS Map Manager as described in my book.
On the bright side, my existing basemap does seem to be intact! My apologies if I got your hopes up for something both free AND easy.