BuyDig.com offers the refurbished Audio-Technica QuietPoint Active Noise Canceling Headphones in Black, model no. ATH-ANC3BK, for $29 with free shipping. That's the lowest total price we could find for a refurb and $30 under the cost of a new unit. These headphones are purported to cancel up to 85% of background noise and feature a frequency response of 15Hz to 22kHz.

A 90-day warranty applies, although it's not clear who supports it.