For something you'll use for hours on end and everyday of your life, I wouldn't try to cheapass your way on a mouse. For something like this, you really get what you pay for.
I've gone thru half a dozen cheapo optical mice before settling down with a MX518. Was able to get it for like $15 after a $20 MIR.
My best advice is to check your local Best Buy/Staples/Office Max.Office Depot ads, or even sites like newegg.com, zipzoomfly.com, tigerdirect.com or frys.com = or wait for someone on sites like Fatwallet or SlickDeals to post a deal for a mouse
From time to time, woot.com also sells refurbished (no one seems to complain about their quality) Razer-brand mice for $20-30 shipped. Razer's one of the premier companies for gaming-line mice.