Cellular Showroom has the NextLink AX2 Bluetooth Headset on sale for $26 with free shipping. Weighing just 12 g, it's about the same size as a thumb down to the first knuckle if you cut it off. This headset features 8 hours of talktime & up to 1500 hours of standby.

They sent me a sample, and I must say it is really very small indeed. The sound quality is a notch below that of my previous Moto H3 and HS850, but the volume is much higher and the fit is extremely secure. Pics: 1, 2, 3, 4, 5, 6