BlueRigger via Amazon offers the Kinivo Bluetooth Hands-Free Car Kit, model no. BTC450, for $39.99. Coupon code "BBBBBBTC" cuts it to $24.99. With free shipping, that's $35 off list and the lowest total price we could find. It's compatible with Bluetooth cell phones and Apple iPhones and features a microphone, music controls, and adhesive pad for mounting.

Note that this car kit requires a 3.5mm input jack in the car stereo.