This is coming from a guy who was in the same predicament you are in, but a year ago. I have both the Intex 26x52 (I think) and the sand filter that came with it, plus the saltwater system that we purchased separately to go salt:
http://www.amazon.com/Intex-54611EG-Kry ... intex+salt
If I could do it all over again, I'd not purchase the above. The cartridge filter from Intex was just a pain, and my water was always ugly. It wasn't until I used the sand filter that I first got my water cleaned up (well water).
That being said, you could go with:
http://www.amazon.com/Intex-54601EG-Kry ... intex+salt
And put it in line with the pump/filter you receive with the pool, so long as it is the sand one. Elsewise, if you don't for some reason have a pump or filter, I'd give this guy some serious thought:
http://www.amazon.com/Intex-56681EG-Fil ... intex+salt
Long story short, I linked my two systems together and removed the cartridge filter. But eventually, my SWG died (at least I assume it did because it always said low salt despite adding bag after bag after bag). If I could do it all over again, I'd probably skip the SWG to start, and just get comfortable with water chemistry using the info provided here.
Once I was comfortable, I would look at a better grade of product from Hayward maybe. But the idea is, the SWG ups your chlorine level by using the saltwater and electricity to create chlorine. You'll still need to monitor chlorine, and perhaps maybe add some during really sunny days, but the amount you go through will be far less than someone who does not use a SWG.
For me, I am going back to what came with the pool, and adding liquid chlorine to maintain sanity(?). When my SWG died, I wasn't doing a good job of keeping track of chemistry, and the water went way down hill, very quick.