That's largely my experience regarding classic steel road bikes, though you do need to know what you're looking at with a complete 2nd hand bike.
My example is my Raleigh Royal, which I built up from just the frame using mostly
eBay parts - approx £250 in total, excluding the saddle (I put a Brooks Cambium on it, so it's not fair to include that in the comparison).
I'm happy with what I have because every component is just what I want, but I've seen very similar Raleigh Royals in what look like excellent condition selling for less than half that.
In fact, I saw one a few months ago that looked functionally as good as mine and cosmetically better. There's obviously no guarantee, and it might well have needed some work and some replacement parts. But it went for just £75.
It was local and I almost bid on it myself with a view to stripping it and selling the parts, which I conservatively estimated should fetch at least £150 - but I couldn't bring myself to effectively destroy such a nice bike.