Patty-If you like the way this looks and want to do something cheaper then try chipboard. It is like cardboard, but acid free. People use it all the time for scrapbooking. Here is a link to 50 12X12" sheets for $12.00 plus postage. They have 4 available, so you could get 200 if you need that many and could probably get a break on shipping. I have purchased this for scrapbooking and think it might serve your purpose.
http://cgi.ebay.com/12-x-12-Chipboard-White-50-Sheets-032-12x12-Scrapbook_W0QQitemZ250261697751QQihZ015QQcategoryZ 11791QQssPageNameZWDVWQQrdZ1QQcmdZViewItem