When I bought my truck, one of the first things I did was trade out the factory tires for better off road tires. It gets a little sloppy at the farm and deer lease when it rains. My truck came with 20's and the Nitto Trail Grappler tire I wanted was $80 per tire more for a 20" versus an 18".
Not being fond of 20" tires in general, I asked the tire store to put any 18" rim on the truck that the had in inventory that met my stock rim load ratings. The 18" rims cost me about $140 each and I ended up selling my stock 20" rims for $150 each.