you are missing a critical part of the equation. Is that over all time and all sites, or one site per day (that would be fantastic) or all sites per week, per month, per year?
When I started 1$ per image per month for all agencies combined was sort of the standard rule of thumb. It is a lot lower now. The total of number of downloads depends more on if you are on mostly subs sites or ones that are more credit based - although that is also going towards all subs these days too.
If you look back there are some interesting posts here re: overall averages at SS gleaned from their SEC filings.