Doggus:
Besides the C'dale, take a look at what Burley offers.
Road tandems in your $$ range: Aluminum framed, Tamburello @ about $1800; Tosa @ $2000. Cro-Moly: Duet and Rumba (same price range).
If you want on-off road capability, the 26" wheeled Samba is a great value @ $1500 or the Rock 'n Roll @ $2,000.
Another thing to consider, if you will not be doing any single-track stuff, is a road tandem with heftier tires for an occasional dirt road riding.
As you suggested a 26" wheeled tandem would work by switching out tires for on- or off-roading.
Pedal on TWOgether!
Rudy and Kay/zonatandem