Most other specifications are more important than VRAM, such as number of cores, clock speed, cooler design and power consumption. To make things easier, there is a tiered list to give you a basic idea. http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107-7.html Keep in mind that this does not compare the finer distinctions between each manufacturer.
If you want to make the trek down, Microcenter either in downtown Chicago or in Westmont usually has really good deals on open box GPUs. Both of my 290Xs I bought in October of last year for $330 each in open box format.