Amazon has this Plantronics M55 Wireless and Hands-Free Bluetooth Headset for only $19.79 (Reg $49.99) and Prime Shipping. It is compatible with iPhone, Android, and other leading smartphones and features DeepSleep mode to extend battery life and voice commands for answering/ignoring calls.
If you are not already a Prime Member you can join with a 30-day free trial of Prime, as a student with Prime Student, or as part of Amazon Family.