I'd *much* prefer if it were free.
EDIT: Hah-hah! *victory boogie* I found the perfect thing, after many hours of searching. :-) http://www.seekingsolis.co.uk/rpg_archive/ has maps of a huuuuge city, with the tunnels and sewers underneath and everything. Exactly what I was looking for. Of course, in the search for a decent map/map generator I also found beaucoup other useful and nifty programs, so I consider myself ahead of the game.