Hi, this is Raymond, the owner of the AdMob Plugin.
The AdMob plugin is FREE.
If use it in Intel XDK, Add a Third-Party Plugin (Get Plugin from the Web), input following info:
Plugin ID: com.google.cordova.admob
[x] Plugin is located in the Apache Cordova Plugins Registry
If any problem, please feedback to github issue page.
And, if you are monetizing via this plugin happily, donation is welcome.