we went in 2002 so my info is old. we stayed at cody because of the cost; problem is that u are still a long way from yellowstone.
jackson hole is expensive and abt the same distance (as cody) but u go thru the titons to get to yellestone (very scenic).
ok, it took us 3 days to get up there from ne la. KC was first stop. we could probably have made it to rapid city the second day but it was late and we stoped east of there (murdo comes to mind...there is a car on a pedistle there and a car musium).
we liked mitchel (corn palace) and got a free glass of ice water at wall. south dekota was out favorite. (Custer St park, hot springs, mt rushmore, and crazy horse). yellowstone was a little disapointing after that...but still worth the trip.
a must see at yellowstone is beartooth pass that goes into the NE entrance of yellowstone. that made the trip for us (don't pull thru there, it has some tight curves). the road is US 212.
we also made a trip across US 2 thru ND to glacier. my advice, if u get off the interstate, fill up when u get a chance. on 2, the stations (for diesel) were few and far between. interstates aren't a problem.