GTA 4 for the PC was released around 7 - 8 months after the console version. GTA 5 may or may not follow that same timeline. Regardless, I am very confident that it will not be released this year.
If whatever graphics card you currently have is good enough to play whatever games you are playing now, then my advice is to use the time between now and whenever GTA 5 for the PC is announced to save up even more money.
I played GTA 4 using a Radeon HD 5850 @ 1920x1200 resolution. The HD 5850 is more powerful than any $80 graphics card on the market. I was only able to play the game with medium graphics quality and frame rates mostly in between 24 FPS to 35 FPS from what I remember.