I personally have a Creo scanner which unfortunately isn't being supported by Kodak software wise anymore but still puts out amazing scans. As long as i don't upgrade to Lion, I'm good. Epson makes some good high end scanners as well... just not like a Creo.
The reason you don't "just use" your digital camera as the other poster suggests is because you aren't getting enough information to enlarge to the sizes you want to make a really professional grade print for the artist.
If I take a shot with my 1Ds Mark III of a large piece of work in a single shot, then try to blow it back up to the original size, it will be a poor reproduction of the original. Just because someone can shoot with a mark II or III doesn't mean they got the best file to reproduce from. I have seen stuff come in that was shot just like that and just using my flatbed scanner my prints would run rings around that print. I made a comparison print of these different methods and my Creo was almost a match for my Betterlght in the studio. I also scanned a 4x5 transy and compared it to scanning the original and shooting with the Betterlight and the transy came in last.
It all comes down to garbage in, garbage out. If you print mediocre work for your customers and they don't know any better, than you will be a god to them. Try that with a customer who knows the difference and that will be the last time you do any work for them.
If you want to do the best you can for them, then you need the best you can afford.
If you try to print up to 40x60 from a digital mark III shot of an 8x10 piece of art, I guarantee it will fall apart at that size.
Just for grins and giggles, go to the Betterlight website and check out their stuff. http://www.betterlight.com/index.html