I think it is rather normal to suffer sticker shock when looking for a "real" bike. It was a lot harder for me to pay $600 for my Trek 1000 than it was to pay $1600 for my Trek 5000.
Some of the Schwinns were pretty decent bikes for their day. In fact, some of them were outstanding. A halfway decent Schwinn Paramount can go for over $1000 on Ebay. What kind of bike do you have. There might be some upgrades you can make that will make your commute more pleasant. If it is a 10 speed, it might actually be older than '81. By 1981, most bikes came with 6 speed freewheels. Can you post a picture?