Banggood offers the Xiaomi Bluetooth Sport In-Ear Headphones in Black or White for $34.80. Coupon code "8bd1ff" drops the price to $27.84. (You'll need to be signed in to apply the coupon.) With free shipping, that's the lowest price we could find by $8. They feature a microphone with in-line control, Bluetooth 4.1, and up to seven hours of playback per charge.
Note that this item ships from China and has an estimated shipping time of seven to 20 days.