I once looked into their financial statements and came to the conclusion that per article published, they had about $2500 in costs and $5000 in revenue, so 50%

I once looked into their financial statements and came to the conclusion that per article published, they had about $2500 in costs and $5000 in revenue, so 50% profit margins. If you look at the price of comparable PLoS journals (i.e. not PLoS ONE), the publication costs are also about $2500, so I think this is in the right ballpark.