Pretty universally $140 plus shipping (a bit cheaper at bookstores), doesn't go on special often.
Amplifier for high end headphones, as well as a better quality dac for your computer. (Acts like a sound card).
Good reviews on head fi.
I ended up going an Asus Xonar DG soundcard instead because I'm cheap, because my a900x don't need a meaty amp, and I'm not convinced music amps are worth the extra cash for gaming.
I can't comment on the price but have the E17. Nice bit of kit.