Today I got a large photo sale for $ 1,20.  I guess the differences between royalties is because of promotion etc but I always get between $ 2,10 en $ 3. But now I really wonder how it can be this low. Anyone?

You can read some more about the dismal per-credit prices at iStock here

It's possible that things may have dropped even lower - I think as some of the big buyers got really upset about prices (esp. Vetta/Agency) begin jacked up they offered big discounts, beyond what you can get by buying directly from the site. As iStock does not make it easy for contributors to find out these things we can't really track what the average price per credit is - and whether it's going down or up over time.