One of the guys is contemplating a visit to the Grand Canyon, but I'm not sure if it'll just be a massive expensive tourist trap despite it's natural epic-ness.
The natural epicness was indeed epic.
We went for a drive out to the Grand Canyon while we were in Las Vegas in 2003. Don't know if much has changed since then, but the only expense we incurred in visiting the Canyon was the fuel to drive out there. It was a few hours drive each way (though not a lot in the big picture)... and we found a traffic jam in the middle of nowhere!
We did get to watch an awesome thunderstorm over the Canyon though.