I would go with BFG AT's 285/70-17's. They are about $200 each.

 

Just got off BF goodrich site, they now have the AT KO available in a 20. I am still trying to find prices but just wanna give everyone a heads up!

 

I just bought a 2004 RAM SLT Sport that was on the lot with 17"s. I don't do a lot of anything but I liked the 20"s and I wanted the 3.55 rear diff. They swapped them for me for ~1180. That should give you a rough idea of invoice on the polished 20's.

Shrek