I bought a Target Alpha that was local for $800.00 and it is a title in demand Cabinet 8.5 Playfield 8.0 and Backglass 9.5.
If I had to do it all over again I would not have paid more than $700.00 as there were items that did not work and the guy had it 19 years and never serviced it so I had to shop the whole thing out.
The Hang Glider is a good title for Bally and the Cabinet and Playfield look good. I would offer $500.00 if you really like the game and it works 100%. If it has mechanical issues $450.00 and that would be more than fair to the seller as the Backglass will need to be replaced, at least for me so I would tell them that as well.