I'm working on building an application that will appeal to a specific but rather dedicated niche. I'm trying to figure out how best to monetize; simply selling the app for $1.99 or using advertisements. However, I simply have no idea how much money the ad-supported model translates to. Is the general consensus to use AdMob or iAds? What kind of returns are made on ads per user? Is there any studies or statistics I can refer to to get an idea of what I can expect depending on my users' usage patterns?