I am pretty judicious in my use of conditioner (because I like the good stuff, too). It will take me a couple of months at least to go through a bottle of One C if that's all I'm using. But I don't condition every day. I condition every two or three days. And I can spread it out further by rotating lesser brands into the mix once in a while.
I use a lot more conditioner to CO wash, so I keep that one cheap and I don't CO wash every day. I would say one bottle of suave lasts me almost a month, washing twice a week.
My conditioners are more expensive and a little goes a long way for me. I would say that, at this rate, my liter Regis Olive Oil Conditioner will last about two months. My Elucence MBC will probably last longer since I've just been using a dab as a leave-in.
with the cheap conditioners depends on if my son gets to the bathroom without me noticing, he's going through a cleaning phase and thinks conditioner is perfect for cleaning the bathroom, but luckily only with the cheap VO5 stuff so far, knock on wood.
We go through about a bottle of VO5 a week sometimes less, but we got 4 curlies in the house too, so . . . .
My more expensive stuff are luxury for me, I can't afford them all the time, so I make them last as long as I possibly can. my last bottle of Devacare lasted maybe 3 months. Making them stretch so long is the only way to justify the expense to myself.