What the best pc case (up to$250) that has good airflow and it is pretty big (big enough to sli 680s) it can be any
if you're going to sli, then get the HAFx. has a gpu duct and gpu supports, plus it's a big case
Depends on what you want out of a case. For example do you want to full custom watercool, AOI water cooler, or just stay on air. Or would you like hot swappable HDD/SDD cages. I think you should look at NZXT, CoolerMaster, Corsair, Silverstone, Thermaltake,Fractal, BitFenix, and Lian Li and choose your favorites for each brand then compare and contrast them then choose the one with the features that best suit your needs. All of those brands have good airflow options in that price range and by adding fans in a lot of those cases you can optimize for positive airflow.