Sears.com sells two "mass-market" tandem bicycles. One is $250 and the other $180! The more expensive model has an aluminum frame and the cheaper one a steel frame. It would seem that a tandem would be similar to a worldbike in stress on frame and components, and so a worldbike should be possible to manufacture in similar quantities to a tandem for a similar price.

This also makes me wonder if it would be possible to build a FreeLoader frame that fits onto a tandem in place of the rear seat, so the tandem could be quickly converted or unconverted for carrying big loads instead of the second rider.

http://www.sears.com/sr/javasr/product.do?pid=00611135000

-- Ralph