The deal Chris Roberts made to the backers is that he would give everyone who pledged before the second anniversary (in 2013) alpha access (because at that time, CR didn't know he'd get some 70 million in funding, and early access is really expensive for them). Now all post 2nd anniversary pledges no longer come with alpha or beta (because, again, he made a promise, and they can't provide free beta/alpha for everyone).
If you just want the game, you can spend $30 and be done with it. You won't get any backer bonuses, though, which means you mind as well just wait until the game comes out in a couple years or so and spend your money then if you like what you see.