If it's free and you're really after eyeballs, you might considering utilizing methods that give you a higher reach. I'd think about websites with a low CPM/PPC rate that reach your demographic. I'd also consider spending that money on developing a good FaceBook integration.
If you games are paid, I'd consider spending a little more on PPC/CPM rates to get a high quality audience.
Any suggestion how to find the sites targeting particular demographics and their rates? Sorry if that sounds like a noob question, we haven't done any advertising before and are not in the US (although most of our new users are)
* use Adwords to advertise there,
* go direct to the sites and see if you can score better deals,
* use various websites like Alexa to find websites just like those sites so you can go direct and talk about sponsorships
* use a combination of the above