I used to grumble to myself about the price of RPG books -- back in the early days of 3rd Edition when I tended to buy everything that came out; I'm more selective these days since I have tons of books on my shelf I will never use -- but considering that 20 years ago I bought all my 1st Edition books new for $20, and now the WotC releases are generally $30-$40 bucks, I don't think prices have gotten too far out of hand.
Consider mass market paperbacks for comparison: 20 years ago I could buy them for $3-$5 on average, now they're upwards of $7 and $8. I have a mass market copy of The Dark Tower VII (came out this year) that's got a cover price of $9.99. I also have a copy of The Stand (Complete and Uncut, printed in 1990) that's got a similar page count and a cover price of $6.99. Publishing, just like everything else, has gotten more expensive.
Right now I'd say that I'm happiest about my purchase of Fantasy Flight Games' Grimm d20 mini-game. I got it for $15 new, and I'm getting ready to run my second big game for a large gathering of friends, so I'm definitely getting my money's worth.
For my regular D&D game, though, I get the biggest bang for my buck from my Dungeon subscription and several Dungeon Crawl Classics modules.