Normally, the Standard Edition for GameMaker Studio costs $49.99 but for a limited time, it's available for free. After downloading, just register an email address and you'll be sent a key.
Also through March 2, 2014, the upgrade to GameMaker Professional Edition is $35, down from the usual going rate of $99.99 -- "simply enter your Standard license key when checking out," according to YoYoGames. Of course, it's the modules that start to add up, but this free version is still one of those offers where there's really no reason not to grab it while you can.
When I think of GameMaker success stories, I think of Derek Yu (Spelunky), Tom Francis (Gunpoint), and Jonatan Söderström (Hotline Miami) -- these three rocked it. In time, you can too.
GameMaker Studio Standard Edition Is Free For A Limited Time [GameMaker Blog]