There is a "game source code" Humble Bundle deal going on now. For $12 you get Game Maker Pro, the Android module, as well as the source code for games such as Stealth Bastard Deluxe.
I am no Game Maker fan, but it is interesting to look under the hood of these games! And it can't hurt to expand your developer's tool box. And the price is rather low indeed.
https://www.humblebundle.com/weekly