Please note this is not a Steam game. It will be digitally distributed via Rockstar's own digital distribution system.
This is currently the cheapest place to buy the game, according to price checking websites and Steamlocks.tk.
There will be some caveats with importing a game from a cheaper region however. Rockstar has warned that there will be restrictions with DLC's — an US copy of GTA5 tied with an European PSN account cannot redeem any DLC's in Europe.
However this only so far applies to consoles according to Rockstars support page and there is no info yet pertaining the PC copy of the game.
If you are only interested in the BASE GAME only and do not think you will buy any DLC's, go ahead and buy.
If you'd like to buy DLC's in the future, you should twiddle your thumbs and wait until the game gets a full review by TotalBiscuit or something.
-How to buy-
Download Hola Addon from Chrome web store and use the N. Americas or Brazillian region to make a purchase.
And they just lost my purchase.