Probably not worth much.
At your budget point, I would not worry too much about vram specs. That is all bundled into the relative performance of each card.
Even at the high end, vram does not seem to be any performance issue.
Read this: http://www.pugetsystems.com/labs/articles/Video-Card-Performance-2GB-vs-4GB-Memory-154/
You might consider using integrated graphics and see how you do . You can always add a dedicated card later. With integrated graphics, you will be able to set the amount of ram to be used as vram for graphics.
Trying different amounts would give you a better idea of how sensitive your games are to vram.