You can get a sense of advertising fees by looking at comparable newspaper ads and industry trade magazines. Even take a look at billboard or radio ads. Custom ads will be an order of magnitude higher that what you get from Google.

I wish I had a deep and thoughtful answer, but a simplistic one is that we do get to keep 100% of the revenue for the ads we sell so in that sense we make more.

Because our content is so specific, ads which are relevant to the content end up targeting the user because you wouldn't be spending time on the site unless you care about the content.