With new seat and new chain, with everything tuned up, I would say around here it would be worth $160.
These were from GT's Streamline series. From a sales viewpoint, the whole series was not successful. GT did some customer research and found that a swept back handlebar was much preferred by the target buyer in this price range, compared to the straighter bar found on just about every other brand's hybrid bike. Despite this, dealers didn't embrace it. And if the dealers didn't embrace it, the bikes never got a fair shake in front of the consumer. The bikes setup would probably sell better today than in '99.
Also, the Airstream model had to have its name changed because of the travel trailer company with the same name and the conflict that caused.