Because less than one of every l,000 bicycles is a tandem, even the cheapest two seaters are affected by the high costs of limited production: non-robotic welding, special tubing and unusual parts. The very cheapest tandems, at $600, cost six times more than a $100 single bike with a comparable level of performance. As prices rise, however, the cost differential of building a tandem diminishes. For example, a $1,600 tandem is only four times as expensive as a $400 single with the same performance. If you are willing to spend more, the differential continues to shrink. A $2,400 tandem will perform like an $800 single (3:1), and those who spend over $3,000 will find tandems cost no more (and weigh less) than a pair of $1,500 singles (2:1).