First off, I haven't seen this forum as a source of cheap bikes.

Here's one in the right price range, though:
http://cgi.ebay.com/Columbia-2-perso...QQcmdZViewItem

Here's one in the right state:
http://cgi.ebay.com/BURLEY-RUMBA-TAN...QQcmdZViewItem

I wouldn't have hopes of lasting happiness with any cheapo bike unless you just get a steal somewhere. The old ones are old and 1-speed, there are new cheap ones (see ebay), but they can't be too great, so don't expect a lot. It's sort of like looking for a $100 car...they're out there, but don't expect it to be a great car.

If Craigslist covers your area, keep checking there- I've seen several old and/or cheap tandems pop up here in the Dallas area in the last week.