I know everyone has different means and so values their entrtainment dollars differently, but I tend to go with the movie model: if I go see a movie, I get about an hour's entertainment for US$5. If a movie is bad, I am disappointed and if it is good, I am happy. So generally that is how I value entertainment overall. If I buy a video game for $60, I expect to get 12 enjoyable hours out of it. If I buy a console for $600, I expect to get an additional 120 hours out of it (good thing I bought Skyrim, then). Similarly, I expect that a $60 D&D book should bring me 12 hours of enjoyment, between reading it and using it in play. If I buy that book twice because I want to use it on Fantasy grounds (which happens a lot) I expect that much more enjoyment.Nobody has to buy any D&D product. I don't begrudge them making a reasonable profit. If I get 6 people together, the hours of entertainment we'll get out of the investment is well worth the cost. Everyone will, of course, have to make the judgement call for themselves.
If you want to talk about overpriced niche products, the "mini" from WizKids for Demogorgon makes sense. A new boxed set for $60 just isn't in that category for me.
By an large, D&D is the best return on investment I have ever seen in entertainment dollars.