All excellent budget recommendations above. If those are still too expensive, there's the Behringer PP400 phono preamp for $24.99 at LP Gear. Just keep in mind that you get what you pay for, and there's only so much performance you'll get out of a $25 phono preamp.
http://www.lpgear.com/product/BEHRPP400.html
http://www.lpgear.com/product/BEHRPP400.html