Quantcast's traffic / reach and demographics measurement are free for anyone. I am aware of nobody that pays us for website traffic measurement or website demographics measurement, and I work on the demographics at qc. I think comscore charges, or perhaps used to charge, for their measurement product, but I could be mistaken. If you don't have us confused w/ comscore then I have literally no idea what you're talking about.
The above said, I'm just a dev, and you should not take that as Quantcast's official position on anything. If you want an official position you should ask our spokesperson.
Also, fyi, it's alexa.