I am afraid you will have to create a plugin for iOS yourself to use Admob or other ad network. Epic is probably busy with more profitable things than helping us. Luckily, latest stable release on github behave better with 3rd party libraries in iOS plugins. I’ve not been able to make Admob work yet (not even the example plugin for TapJoy; it builds fine but always crash on device for unknown reasons). Let me know if you manage to make it work 
Meanchile, you can try to make profit with in-app purchases. My 3 most downloaded apps have been several months not making profit at all for this reason.