I would gladly (and highly profitably) run a for-profit which "manages the peer-review process" for GBP 1 per article.
People will evenutally solve this problem parts at a time, but I wouldn't put a £1 per article price tag on it yet.
Their costs aren't low, and presumably they don't make profit either. It's fair though, although i might say a bit expensive for authors from developing countries. You want to have a barrier in publishing and a good review process, and it's more fair (esp. to students in the developing world) to charge the authors rather than the readers.
Hopefully, if we have competition among open-access journals even the costs may go down.
I use 'surplus', not 'profit' because PLoS is a non-profit. They can build up reserves to guarantee continued existence in times of hardness, or for future growth (for example, they may need money in the bank to rent or buy offices, or to make them more attractive to prospective employees (who is going to work for a non-profit that, every month, hopes to be able to pay your salary?)