You'll get a better-educated guess in the Classic and Vintage Bicycles: Whats it Worth? Appraisals and Inquiries forum.

Narrow frame tubing and the joint style makes it look like one of Schwinn's flash-welded frames, and since the photos make it look like the front fork blades are flat rather than tubular, I'm guessing a Varsity.

Unfortunately, if my guess is correct, it's an entry-level bicycle that was mass-produced in astronomical numbers. Unless it's in extremely pristine condition, these kinds of bikes seem to go through craigslist at $75-$150 asking price.