Joined: Jul 2010
Posts: 858
Likes: 6
From: Metro Detroit
Bikes: Bertoni Corsa Mondiale, Bridgestone T-700, Miyata 700 GT, Trek 600, Trek 560 Professional Series, Chrome Panasonic DX 2000, Peugeot PH12, Peugeot PX10, Schwinn World Voyageur, Schwinn Circuit, and Schwinn Voyageur
Vintage Trek bikes are great rides! Although I've never owned a 520, I have owned better models and payed much less.
It is hard to estimate value without pictures. I can't tell you what it is worth, but I can tell you that $500 is too high.
I would keep looking.