We bought a new KHS Milano tandem on sale for $1695 from Crank2 Performance.
I didn't want to spend $1000/1500 to buy used and have to make repairs or upgrades on maybe a 10 yr old bike. The large oval tube aluminum frame is very rigid compared to a Trek we borrowed for a while and weighs 42lbs with spd pedals, dual 203mm discs and wedge bag. This bike comes with a front disk compatible hub and fork and a rear wheel that will take a screw on spacer block for a rear disc. The frame also has the boss for the rear caliper to mount to.
And the admittedly lower end Shimano Tiagra shifters have a cool feature for tandems having shift position indicators on the tops showing what gear your in. All in all we are quite happy with the KHS as a first tandem and it's been trouble free for over a year. I reccomend you look into the KHS Milano before you go used.
This link has the specs.
http://www.crank-2.com/store/departm...les-Framesets/