Restored 70's Schwinn Twinn Tandem
First off, it's gorgeous - beautiful work.
As to value... first, understand I am no expert, this is just my opinion; and that and 99 cents gets you coffee somewhere cheap. So FWIW...
My guess is that you might get $500 - 1,000 ??? I'd guess it will depend on many things...
- possibly the biggest is getting it in front of some buyers who appreciate the historical context of the bike, and the craftsmanship of your restoration; and have the cash, the motivation, and some immediate desire to move now, not later.
- your location- a bigger city, with a longer season, and more places+times to ride, will probably allow you to get more for it.
- if you can get more than 1 motivated buyer in, so that you can legitimately say, "I gotta get back to this other guy." In my experience, the guy who can say "well, I think I'm gonna sit on it, think about it for a little while" almost always gets the better deal, whether that guy's the buyer or the seller.
- timing: if somebody's jazzed about it as a Christmas present, that'll move it in December. If not, I'd be inclined to wait til it's spring where you are- people are usually short of cash Jan-March, and in cold weather few people are thinking about buying bikes.
Nice job, good luck, and CONGRAT's on your engagement.