I live in Austin, 1 1/2 hours and a world away from SA. SA is big, not really big city like NYC or Chicago, it's spread out big like Phoenix. Lots fo stuff to do around SA, Six Flags, Sea World, yes a Sea World in the middle of Texas, fishing (my favorite ) and plenty of Mexican culture. Great Mexican and Tex-Mex food, lots of stuff happening downtown year around.
As for COL, I think it's similar to Austin, maybe not as high. Like I said, it's a large place, so you can find rent rates in all ranges. New Braunfels is up I-35 a bit, 1/2 hour or so, and it's a cool place too. Lots of people liek to live in the San Marcos/New Braunfels area and commute.
Check out www.sa360.com for some more info. I don't know a whole lot abotu SA, just go there for concerts mostly, and drive through on the way to go fishing down in South Texas.

Edit Your profile says you're in Houston, so you probably know about as much about SA as I do. Either way, it's gotta be better than Houston, right?