While there will be a range, condition is king. A low price on a thrashed bike will probably cost more than you anticipate to replace worn out components.
Best used bikes come from people who bought one and then decided they didn’t really care for it and it sat in a garage for some years. Aside from geometry and technology improvements, you are buying a new bike for a well depreciated amount.
If course this changes as decades roll along and nostalgia turns it into a rare vintage work of art for a particular generation that is worth more than one can possibly imagine.
John