Watch www.chainlove.com. They occasionally post some killer deals on bike lights there, like a Light & Motion Vega for $75 (normally ~$200)!

Good lights are, IME, a worthwhile investment. I love this bike light "shoot out": http://eddys.com/page.cfm?pageID=493. It really defined for me what I was getting by spending more, and what I could expect. The shootout pics show the Cateye EL-520 to be pretty darn bright- might be a really good choice!

Good luck shopping!