I ran into this problem the other week. I was trying to buy 5 pi zeros for a few projects I have in mind and a couple of backups to have lying around. Couldn't do it. Very frustrating.
Anyone needing to buy several Pi W's should look into the Orange Pi Zero. They also play some games with the shipping cost, but at least the shipping cost per unit goes down the more you buy. Buying 5 would run you $10.60 each, and 10 would cost $10.30. (All US shipping prices from AliExpress)
The main thing to look out for is that it doesn't have HDMI out, only two headers for composite out. I imagine most people plan to run them headless anyway, but unless you have something that can display composite video, it can be a pain to set up at first.
Another option is that when you buy from Adafruit, you can buy one of each version. One Zero, one Zero W, and one Zero WH, for $29 plus shipping. You can then buy a USB WiFi adapter off E-Bay for about $1 shipped, and as many USB OTG adapters as you need for less than $1 each. Depending on shipping, that puts you in the $11-$12 per board range.
The main thing to look out for is that it doesn't have HDMI out, only two headers for composite out. I imagine most people plan to run them headless anyway, but unless you have something that can display composite video, it can be a pain to set up at first.
Another option is that when you buy from Adafruit, you can buy one of each version. One Zero, one Zero W, and one Zero WH, for $29 plus shipping. You can then buy a USB WiFi adapter off E-Bay for about $1 shipped, and as many USB OTG adapters as you need for less than $1 each. Depending on shipping, that puts you in the $11-$12 per board range.