Where are you buying your tires? Those prices seem really high, I've never paid more than $180 a tire online. I searched the Continental Extreme Contact DWS on TireRack and the 235/45/17 size are $148 each. TireRack will deliver to a shop so you don't have to transport them to a tire shop.
I've had Continentals in the past and was happy with them, right now I am running BF Goodridge g-Force. I always seem to go through two sets of rear tires for every set of front tires regardless of brand. I normally look at the reviews on TireRack and balance price and performance.
