Accessory Genie via eBay offers the Gogroove SonaVerse Color-Changing LED Desktop Speakers in Grey for $14.99 with free shipping. That's the lowest total price we could find by $5. These 6-watt speakers feature a frequency response of 250Hz to 20kHz, 3-foot USB cable length, and a 3.5mm audio output cable.
mwave offers the Microlab 2.1-Channel PC Speaker System in Black, model no. M850, bundled with a $7 gift coupon for $39.99 with free shipping. Assuming you use the coupon, that's the lowest total price we could find by $17. It includes a subwoofer and wired remote control.