Find a local bicycle store which has tandems to rent. Rent more than once. Try different types, road, cruiser, trail. If you buy a tandem that is not nimble and fun to ride you will only ride it a few times. Unless you are really lucky, you won't find a light weight, responsive tandem with good quality shifters and brakes for less than $500. Where ever your marriage is headed, it will get there faster on a tandem.