I point to PLoS as essentially the model you're asking for. It's a non-profit publisher started by open-access advocates working as researchers. There are no investors making a profit and they're mission is to spread open-access as a model, and they end up charging $2200+ per article for most of their journals. If that's the number they came up with, then I'm led to believe that that's what it costs to publish a journal, at least in the biosciences. As I said, there are small journals that operate for free, but if you look at large-scale open-access operations, started by idealists, I don't think you're going to find any that sustainably gets by with article charges less than around $1500.
For comparison, when I looked at Elsevier's finances, it seemed that they're charging roughly $5000 per article and half of that goes to their operations and half is profit. So their costs are roughly the same as PLoS, but they charge twice as much in order to make a substantial profit.
As for why I felt the need to correct you, I think it's because I think in general people ignore the real monetary costs associated with open-access publishing. I believe that author-pays open-access is the way of the future, but getting there will mean that researchers will have to find ways to pay these fees when they haven't had to pay before. In principle, this just involves redirecting money from subscriptions to pay author charges and there'd even be money left over, but actually performing that switch across thousands of institutions is not simple. Too often I run into the attitude that for-profit publishing is charging money for a trivial job, and so people wonder why it hasn't been replaced. However, the truth is that they're performing an important and real task with real costs, while also over-charging for it, and that's not going to be replaced overnight.