A couple of other great sources for marbled papers are:
Multi-Cut USA, Macon GA, a division of Ocumulgee Arts @ (800) 521-8974...very reliably in stock and inexpensive.
Harvey Fabrics, NY (800) 221-1096...slightly more unusual papers.
Both sources will sell you a sample pack of their papers.
Search the web for marbled papers and you'll come up with some really fine marblers with unusual papers.
I agree with Richm...use PMA as an adhesive and cut the strips by hand, or use your mat cutter (the manual variety)
Miter the corners, rather than overlapping the paper for a more professional look.
Marbled papers are a really simple "add-on"; A dollar a ui, retail, is about right, depending on your market and the paper you use.