Walmart offers the Logitech S-120 Stereo Speaker System, model no. 980-000012, for $7.25 plus $1.97 for shipping. (Site-to-Store pickup is also available.) That's the lowest total price we could find by $5, outside the price below. (For further comparison, we saw an open-box unit for $3 less in February.) These speakers feature a 50Hz to 20kHz frequency response, 1.15 watts RMS per channel into two channels, and 3.5mm headphone jack.

Don't mind an open box? newegg has an OEM unit for $9.99 with free shipping.