If your looking at Tandems you better get ready for sticker shock, the links below tell the story. If you can find a used trike tandem and they're far and few between you can look at $3500 to $6000 depending on the model and age. Try looking at Hostel Shoppe http://www.hostelshoppe.com/ they have both Greenspeed and WizWheel tandems along with a lot of other regular trikes. As for your last ? about pedaling , the WizWheel has the option of an IPS so the wife doesn't have too maintain the same cadence as you.


http://www.greenspeed.com.au/gtt.html
http://www.terratrike.com/tandem.php