How to add Google Ads or similar in "AIR for Android" application?

Hello,

I have developed my android application (AIR for Android) in Flash Professional CS5.5. It's completed and fully tested on multiple android phones. Now I want to add Google Ads in my application to make some money.

What I already know:

I know that Adobe provides AdMob native extension API which allows you to add Google Ads in your app. But unfortunately, it's not free.

What I want:

I want a free resource through which I can add ads in my application.

Please guide me how can I achieve this?

Thanks in advance,

momersaleem