I had a 1983 Trek 520 that I bought new (it cost $365 in the fall of 1983). As Neil said, this was the low end of Trek's touring line. Reynolds 501 tubing, low end parts, limited braze-ons, rode like the tank it was...
In 2005, I ended up giving the bike away. Now that I see what people are willing to pay for these "vintage" bikes, I wish I had held on to it.