Well I just got an email from Anderson Pens that Bungbox is going to a new 30 ml bottle, along with a price increase, so the current 50 ml bottles are discontinued. For at least that store. Other Japanese web sites having custom Sailor inks still list their 50 ml bottles (now often square).
At the current prices I've found Bungbox inks to be out of my price range, so a smaller bottle at the same price or more is out of the question.
I personally have plenty of Sailor and Bungbox inks, so I won't have any need to replace them if it ever turns out that I actually run out of ink. Which I don't think is possible for me. I'm sad for those who come along in the future and have heard about these inks, and find them price prohibitive.