Ive been buying Pi Zeros sporadically for the last few months at $5 a pop. There is a web site that tracks their availability:
I've been buying mine from both Adafruit and the UK suppliers. All suppliers deliver within the week. Currently they are limited to one item per order so if all one wants is a Pi Zero, the cost is $5 plus postage which takes it to about the $12-$15 (US) mark. Ideally, I'd love to buy a "bucket" of them ... but I've reached the point now where I have about 4 ready for experiments (and have managed to kill 2 already through gross negligence).
See free book on CHIP at https://leanpub.com/chip