Many of you have heard of the Bella Band which is sold at major maternity retail shops. It normally runs between $20-25, and the color selection is basic. On my search for a similiar product with a cheaper price tag, I discovered the "BELLY BAND" which is made by an independent designer in Canada. She has a full selection on EBAY, but also can accomodate custom colors/patterns. For popular patterns, the starting bid is $4.99, and can be battled out by 4-5 bidders. But for your basic solids, you can easily purchase one for $6.99-9.99 plus shipping. I've worn my basic black band for several months, and it works wonders to keep your unbuttoned pants up. It also adds a cool layering style.
Check out independent belly band crafter: Mili bryon at http://myworld.ebay.com/milibryson/