It's that pesky little duo called supply and demand. People are buying a lot of used games at the high prices and so the prices stay high. Economics 101. Refuse to pay the prices. I shop around and use coupons, specials, promos, and such to keep my gaming habits met cheaply.
For instance, I just bough some new stuff from Toys R Us on a VERY short Buy One Get one Free deal. I got 2 new release ($60) games for the price of one and 2 PS2 games that were 20 each for a total of $20... Recently there was a 25% off coupon from Gamestop. That plus my edge card got me Untold on my PS3 for $12. I picked up Conan for PS3 for $7.50.
Cheapassgamer.com is a great place to look... Another option is Goozex. You can trade games at fair market value for $1 plus the cost of shipping (about $2). It works well...