Do you want to be the next great Indie dev? Well here is your chance, maybe, GameMaker Studio Standard edition is available for free for a limited time. Regular price is $49.99, GameMaker Studio Standard is a significant improvement upon the free version of the software which imposes harsh restrictions on the resources that developers can make use of.
Developers can use their free Standard edition license to upgrade to the Professional edition (RRP $99.99) for only $35 more. This offer ends March 2, 2014. To take advantage of this offer, download and install GameMaker Studio and follow the instructions that appear. To upgrade from GameMaker Studio Standard to GameMaker Studio Professional for $35, simply enter your Standard license key when checking out. Source