I don't think everyone is motivated by price or that it is the only deciding factor. One telling sign for me is that of the last two companies my wife has worked (an ad agency and a magazine) they both used SS.
It sounds like Runeer you are considering exclusivity? When I was briefly non-exclusive, I found that my mirrored portfolios didn't compare in terms of earnings at all (20:1). I feel this was mainly because all of the sites sold rasterized versions which allowed the customer to purchase a small jpeg or something - of course with IS only allowing for the EPS to be bought. I can't justify to myself to sell at SS.
It sounds like Runeer you are considering exclusivity? When I was briefly non-exclusive, I found that my mirrored portfolios didn't compare in terms of earnings at all (20:1). I feel this was mainly because all of the sites sold rasterized versions which allowed the customer to purchase a small jpeg or something - of course with IS only allowing for the EPS to be bought. I can't justify to myself to sell at SS.

$150 month at iStock for one file was great, but no I mean over it's life. My calculation is pretty simple: If I can produce 3 images a day, I'd like those images to produce about $400-$450+ over it's life for the day's work. That's generally what I consider a successful file.