Your best solution would be the i3 with the 750 Ti in that case then, why are you limiting yourself to Sandy Bridge? Can you get one cheap somewhere or are you unable to get Ivy Bridge or Haswell?
getting two exchange offers for my xbox 360 kinect 250gb
will 2 cores hold me back
The problem with the i5 750 is that it is such an old CPU now that more modern dual cores can beat it. The i3 has 2 physical and 4 logical cores. What games are you planning on playing on it? Not many games should be CPU limited, especially with that GPU.
OK, you should be fine running with the i3, plus you can always upgrade on that socket (1155) in future when you get the money. Your GPU is likely to be the limit before your CPU in most games.