mwave offers the Connectland USB-Powered Stereo Speakers, model no. CL-SPK20037, for $9.99 with free shipping. Outside of the price below, that's the lowest total price we could find by $5. They can be combined into a "soundbar" and feature a 100Hz to 20kHz frequency response and both 3.5mm stereo jack and USB port.

A close price: Amazon charges its Prime members $10.40 with free shipping. (Non-members can spend $25 or more to qualify for free shipping; otherwise, shipping costs $8.77.)