If you found a stopper that fit properly could you ferment in one of those plastic jugs that spring water comes in? They look just like carboys.
You have to check what material they're made out of and the O2 permability. Generally, the answer is no. Better Bottles are made of a different plastic than a water jug.
The standard brewers best ale pail is HDPE. (Recycle code 2 which below PET that make up better bottles) Even still, these are not recommended for any sort of extended aging due to oxygen permeability and excess head space. If the plastic jugs are not #1(PET) or #2(HDPE), don't use them. edit: meant as a reply to OP.
I use water jugs to ferment in besides my 1 better bottle-like carboy that came with my MoreBeer starter kit. I use the same stoppers for the water jugs as I do for the better bottle. I made sure they are PET #1. They're also much cheaper, $12 for the 5 gallons of brewing water and a jug, and I don't have to worry about cleaning it because I just exchange it for a new one.
