BlueMall via Amazon offers the iKross Bluetooth Hands-Free Car Kit for $29.99. Coupon code "IKROSS20" cuts it to $9.99. Plus, Prime members receive free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $6.09.) That's the best price we could find by $13. It features a microphone, music controls, and adhesive pad for mounting.
Note that this car kit requires your vehicle to have a 3.5mm auxiliary input jack.