Mt. Rushmore
West Yellowstone
Mt. Hood
Oregon Coast
Mt. Rushmore. We stayed at Custer's Gulch (commercial) campground for a week which allowed us good access to Custer State Park, Needles Highway, Mt. Rushmore, Crazy Horse, etc. Not particularly inexpensive, but not over priced in the area.
West Yellowstone. We drove down into Idaho about 20 miles to Island Park and the Red Rock RV Park. It is less expensive and is a beautiful area in its own right. The drive into Yellowstone was never unpleasant for us; it was part of the pleasure. If you stay there go down to the area around Johnny Mack's cabin in the late afternoon. There was also a youth rodeo about a half mile down the road which included a chuck wagon dinner. Wonderful.
We stayed at Memaloose State Park near The Dalles, Oregon and made a drive out toward Mt. Hood. That was not our objective on this particular trip but it was a good overnight right on the Columbia River.
Oregon coast: we stayed at South Beach State Park. A very large park, but well spaced. We had reservations for these two Oregon State Parks months in advance of our trip.