If you are looking for originals then they are usually pretty cheap. If you are looking for more modern radial/tubeless options there are lots of threads here that have discussed them. I bought 16" 1991 Suburban 3/4-ton wheels so I could run radials. I bought a set of 4 for $80 at a local salvage yard.
http://www.flickr.com/photos/advance-design_parts_co/8129054429/in/set-72157631867396207