From everything I've read, the only impact a CAI will have on gas mileage is decreasing it. Since you're sucking in more air the computer adds more fuel to keep the fuel/air ratio balanced. Feel free to correct me if I'm wrong on that.
I recently bought an inexpensive CAI off eBay from the seller "chromeintakes" for $65 shipped. I was able to install it myself and it works just as good as a $300 MOPAR one. 90% of a cold air intake are pipes and elbows that are exactly the same no matter which one you buy, the biggest factor in the filter.
My plan is to replace the filter on mine with a brand name one like K&N down the road, and replace the elbows that came with it (they're not metal they're made of some sort of silicone material) with something sturdier when needed. Once I do those 2 things I'll have one that is identical to a top shelf brand name CAI at about half the cost.