Groupon offers the FiiO E17 USB DAC Headphone Amplifier for $109.99 with free shipping. That's the lowest total price we could find by $29, although we saw it for $10 less in April. It features an OLED display, mini USB connectivity, 3.5mm and S/PDIF inputs, gain controls, balance controls, and tone controls.

Also available is the Fiio E10 USB DAC Headphone Amplifier for $59.99 with free shipping. That's another low, by $15, although we saw it for $15 less in December. It features an internal digital to analog converter, 3.5mm and coaxial connectivity, volume knob, and LED indicator. Deals end June 7.