With the funds you have, on android you should not be going with admob. You should try one of the incentivized or non-incentivized services. The non-incentivized ones are better for acquiring users that are more likely to stay. You don't pay for impressions or clicks, you pay for users. It's a good way to climb the New chart in the one month window soon after you release. The new chart is easier to climb than the regular charts and you get some good visibility on it. You can then use that momentum.
I will take a look at it. Please give me a link This week I will discuss with my people a toe test with Facebook. $1,000 is not going to kill us and it give us some real time data. With google I am impressed with how much exposure you can get in a matter of seconds. Now to make it work I think comes for the right ad.
http://devblog.miumeet.com/2013/03/results-of-promoting-android-app-using.html It's explained a bit there. You can see the effect in their summary.