I have had a total of 3 aftermarket leather kits. My first set was from Automotive Leather Inc (you can find them on eBay ID:alileather). The leather is high quality and very thick, very similar to the Katzkin kit I've seen. I got rid of it because I didn't like how it looked. I had a Classic Soft Trim kit that I never installed, their leather is very good, some of the best I've seen. The 3rd kit and the one that is currently installed on my 4Runner is made by Bartlett, the company that supplies the leather to the Southeast Toyota Distributors, which installs them at the port over there. This kit is nearly identical to the leather found on the Limited models. I bought the kits from eBay and installed them myself. They range from $300-400 just for the kit. Installation is a pain though and I do not recommend doing it yourself. But if you feel like you can handle taking your car apart and getting cuts and bruises on your hands, it could save you a lot of money.
My uncle recently priced out installing aftermarket leather in his '05 and they were anywhere from $900-$1400 from independent auto upholstery shops. The dealer usually sends the car out to one of these shops to have the kit installed and then marks you up since they want to make a profit too. Not all dealers do this, but most of them do.
As Uneek suggested, I would recommend the Classic Soft Trim leather. They are a bit more expensive (around $1300 if I remember correctly), but the quality is excellent.