Microphone-only Bluetooth accessory?

[Grimsrud]

I currently have an expensive pair of headphones that I bought for my 5G iPod (Still going strong) a few months ago, so I don't want to buy an expensive new device that will do music and phone calls. I'm currently just keeping my headphones on during my daily commute and speaking into the phone. Is there any sort of small Bluetooth microphone that I can clip onto my headphones or plug the headphones into? I'd really hate to sink $100+ on a quality Bluetooth headphone/microphone device since I bought those headphones so recently.

 

[Missjenna]

What about something like the motorMouth II from scosche?

http://www.scosche.com/consumer-tech/product/2049