You are right, Ivor, to keep these things in perspective. I think the last thing I spent $49 on was a tank of gas--uh, petrol.
Nevertheless, as a booklover and collector with sixty years' experience, and allowing for all those things that contribute to rising costs and prices, I still think fifty bucks is pricey for a book that is probably almost all print (that is, few or no illustrations). Just living in the past, I suppose.
Oh, I know: this particular book is from a small publishing House; and the market is, in publishing terms, quite small, even including the university and college libraries.
So I'll lay out the $49, you may be sure.
Now, when HLG's Volume IV comes out, it will likely be priced over $100, as was Volume III. (Is my memory correct here?)
As for finding a Mahler book in the used-book market, well, the pickings are thin, in my experience.
. & '