Most Windows Phone or Windows Store developers know about AdDuplex (which I am a Developer Evangelist for), and many use them to help promote their apps. They do this either by adding their control to their own apps (earning free ad impressions) or by simply purchasing ad impressions directly. For those doing the latter, their pricing just got a little better, but has a higher starting point.
You used to be able to get 20,000 impressions for $60, which was a cheap way to test them out, but didn’t give you many impressions, and wasn’t very cost-effective. As some developers didn’t have enough money to purchase the larger packages though, they were stuck with this package, meaning they couldn’t get much for their money.
Adjusting to feedback, AdDuplex has replaced that package with a 50,000 impression package for $99. While costing a little more, it is still cheap enough for small devs to afford, and offers a 33% better CPM (cost per thousand)! It used to be $3, but is now $1.98.
Even better, if you currently have a published app with the AdDuplex control installed in it, they are currently giving a 20% discount on all ad packages, so be sure to check it out.