Dreamstime prices depend on the level of the images - level 5 are nearly twice level 0.
Depending on what rights you need, 123rf might be a good option as they allow Limited ELs for select rights and a Print EL, both of which are cheaper than the Comprehensive EL.
As not all images are at all agencies I take it you haven't selected specific images yet. And your question suggests that the actual images aren't particularly important and you're assuming you can get something to meet your needs pretty much anywhere?