Centurion made a wide range of bikes, from entry level to almost pro level. The component group is often a good clue as to the level of the bike. A bike with Suntour Superbe or Shimano Dura Ace or Shimano 600 would be a top model.

And, the condition of the bike is crucial. I have found 1985 bikes that were "like new". Someone got it for their birthday, rode it around the block, and hung it up in the garage. Another bike of that same age may be totally trashed, from top to bottom.

So, you need to research the bike carefully, check out the components, the wheels, and the condition. I see Centurion Dave Scott Models on E-Bay in excellent condition that sell for between $175 and $250. If a Centurion is going to need $200 in repairs to be ridable, that makes its value something closer to $25 or $50.