I've looked into this a bit not for art images, but for photographs of objects.
The advice I'e been given is that Photo-CD is the cheapest and best way to
go, provided you have slides to start with. (It's more expensive with other
media.) You might want to talk to Selma Thomas, of Watertown Productions here
in Washington, who's been working on the project of digitizing some of the
National Gallery collections.
 
Steven Lubar ([log in to unmask])
National Museum of American History, Smithsonian Institution