Here is a random pic off a "high end" stock photo site. Pricing depends on resolution and usage but you can see the list if you scroll down. There is also a pretty big premium for exclusive use.
http://www.gettyimages.com/detail/200250275-001/Photodisc
Now these are just photos - I'd probably value the renderings done by CtrlAltDel a bit higher than just a photo.
That being said, there are lots of ways to get images cheaper. There are sources of stock content that charge only a couple of bucks a photo or less and some are even free. Sometimes it is as easy as emailing the creator - some would rather just give permission than deal with the hassle of billing.
Generally, unless they have been explicitly waived, the creator has moral rights to their work as well which means they must be credited with the work. Stock photos generally have these rights waived as part of the purchase price.
Ultimately, with a creative work, the price is whatever you can convince someone else it is worth.