I guess they take a percentage of your sale. So it all depends on the price at which you sell your domain. I dont think they take 50 $ per sale because then what will happen to those guys who sell it for prices lower than 50 $ ?
But it says on this page that it might be $50 minimum, or I might be interpreting it wrong. http://www.sedo.com/services/prices.php3?language=us
Yes, I think they take $50 at minimum although I have read somewhere that it is not like that anymore. But on the other hand the last time I had an offer for $60 on Sedo I rejected it because there was written that I would get $10 if the name was sold for $60.
I'm moving my best domains to whypark dot com. You get 100% of the ad revenue since you enter your own code. The system pulls in good syndicated content and generates a valid Google site map. You can add pages of your own. There's a nice collection of templates to choose from. And more. The cost is a one time dollar per site. Related to this thread, one of the best features of Why Park is the direct contact form if you list it for sale. No middle-man fees. You can see a domain I am working on at freepersonalhosting dot com. I would post an affiliate link but I'm willing to endorse them without it. However, if you check the service out and like it I'd be interested testing some link trading from parked domains on it. Anybody interested in doing a test with me let me know.
very few domains are sold at $60, because the seller wins only $10. The mininum fee of sedo is justified by the fact that they take care of the transfer and act as an escrow service.