Let's say that your fee site does 5 gigs of bandwidth (and that's probably a bit high) Using your figures, that'd be $7 - you make just one PPS sale & you get $30 which is of course a $23 profit.
Based on that profit margin & the goal of getting one sale, things look good IMHO
I'd throw in the cost of content, but I haven't bought any in so long I don't know what the going rate per pic is - LOL