We've bought a few fonts here and there when we were either trying to match something or going for a particular look and there were no close matches.

The history of font prices dates back to the days of typsetting machines that used pieces of film containing all the characters of a font, installed on rotating drums with lights inside the drum that projected that particular font/character onto a piece of film or photo paper.

In those days, a font could easily cost $300-500 for a single font; bold, italic, narrow, etc were all separate pieces of film that were purchased separately.
I think some type foundries are still of the opinion that they should be paid large sums of money for their fonts, and a lot of designers still do.

Of course, developing a new font that's of truly high quality, with all the individual ligatures (the way specific letter combinations fit together) and kerning rules (spacing between letters) is complicated business that takes a lot of time, so it is fair to pay a reasonable amount of money for a good font. I've found that the free imitations are never as good in terms of their kerning rules and ligatures, so the fonts never look quite as good when the type is actually set, but, sadly, it's also nearly impossible to find a good graphic designer that truly understands typography, at least for less than $75 or $100 per hour.