>>> Buy cel books made of polypropylene. For example, 
two types of "ITOYA Art Profolio" work:
 IA-12-11 having 24 pages 11" x 14"
 IA-12-14 having 24 pages 14" x 17".
 They also have ones with 48 pages but I would advise 
against using them, since they get heavy & bulky when filled.
 ITOYA phone (800)628-4811 / (888) 588-0345 (Canada)
 Web Site:http://www.itoya.com/main.html

The 48 page Itoya books are not wide enough to fit cels.

Also, if you buy from Itoya directly, they charge you for UPS
postage at about $6, plus retail cost of about $13 per 11"x14" book.
I think that you also need to buy a whole box of books, as they 
normally don't deal at the retail level.
It's cheaper to either buy it at an art store or from a couple 
of places that I have seen on the net. 

Metaphor (the smart shopper...)