Cycling induced anoesis
Used bike prices vary by region and depending on use/ condition, so sight unseen I really can't offer you any reliable advice on that. Best bet is to have your LBS appraise the bike while they're checking fit and mechanical condition. They'll see it and know the pricing in your area.Thanks so much - that's a great idea.
As for the models and prices though, any advice?
Re: brands/ models, it's a very competitive market, so in each segment they're all fairly equal. Differences will be primarily in the contact points (pedals, saddle, bars/ shifters). That's why test rides are important. Even noobs can tell when something doesn't feel quite right.
If you do go with a private seller, continue to press them for information, then check Bikepedia.com or the vendors websites for specs. For used bikes, look for something entitled "Archived" for older models.