Just bought a KHS tandem. Basically, this bike: http://www.khsbicycles.com/11_sport.htm.
Paid $250.00. Bike is in Excellent shape. Original owner bought it to ride with his wife who is blind but her interest waned early and it's been garage kept for a few years.
Based on the test ride, I have a feeling that the level of communication with the wife is going to have to reach new levels.