I checked and REI was cheapest @ $10.50 ea. Called my local REI and they had none, but they checked and found that they had 244 in their one and only distribution center. They quoted two weeks for delivery. I ordered my six. But assuming perhaps 2 in stock at each store [JWR adds: Unlikely, given recent events] that’s less than 500 available nationwide. That’s less than 1 for every 12 SurvivalBlog readers… I wonder which future ransacked city their distribution center is in? Hope it wasn’t New Orleans. Kind of unsettling how some things are really pretty scarce already.
Oh, I also have a Product Report: The MSR Chlorine Maker is GREAT as long as you have 6 VDC or a good supply of 3 volt lithium batteries. It came to mind while thinking of “Mr. Coffee” in Costa Rica. The MSR MIOX Water Purifier 
Still the “old reliable” is what I have the most faith in, since I’ve used one since 1976 and that is: The Katadyn Pocket Filter with Output Hose 
Regards, – The Army Aviator