Fair price for backlinks?

This is really just a noob question so sorry if it's obvious.

The comments under a post below said that $700 for 150 backlinks is too low, and the backlinks are going to be crappy, sea-trench quality, which obviously makes sense.

But then I'm wondering, what is a good, optimal price for a single, high quality backlink from a good website.

Comments under that post said $250 at least, but is there a certain price range to look for or something like that?