Sorry no idea. Depending on where you are, if you want to try and figure out what it might be worth, scan through craigslist or your local equivalent looking at 80's "10 speed" bikes in similar shape with Shimano 600 components and look to see what they're going for. Each area is different. If you want to try selling on e-bay (more work for you to deal with, but maybe a better sales price to make up for it), you can do the same thing looking through completed auctions.

If you want to take some time to find out what model it is, this page has links to all the Schwinn catalogs and you could page through them to find one that looks like yours with the same specs. If you're going to try selling on e-bay this additional information (year and model number) will be key.

Are there any stickers on it telling what tubing it's made out of? If there's a sticker saying Reynolds 531 for example, that should be mentioned in any ad you make and might increase the sales price a little bit.