You're in luck. Newegg has free shipping on Wireless Networking equipment until the end of September. Probably a back-to-school special.
All you need is a router, and a Wireless PC Card, and you're set. I assume you already have a modem set-up with broadband, right?
Router = D-Link WBR-1310 = $39 - $10 rebate
Card = TRENDnet TEW-421PC 802.11G = $19