Thats a very good deal on "New". I found the preferences on my Zumo 550 software, set up in mapsource/edit/preferences/routing as "Shortest distance or faster time, and then you can also choose avoidanced roads such as " Tolls, Unpaved, Ferries, carppols, U-turns, combined with a 7 position slider that is either Perfer Minor roads, or perfer hiways.
I am not sure I could do a 100% dirt roads trip in my mapsource, but have never tried.
"Pain is weakness leaving the body"
"Nothings possible until its done!"
"If ya can't afford the fine, take the lead!"