I use
rvparkreviews to check out campgrounds. When traveling, we have found that Passport America will pay for itself in just a couple of nights. Your costs will vary depending on how much you eat out, how much you drive, etc. Despite this, over the past 5 years we have generally averaged about $100/day (that is including groceries) with an average of $30/night for campgrounds. The latter will get skewed quickly when you stay at an expensive spot.
Several years ago I read about the "rule of 3s" on this forum. Great advice - don't drive over 300 miles a day, stop by 3pm, and stay at least two nights every third day.
We generally have reservations at major destinations, such as Yellowstone, then plan the route and have tentative campgrounds identified. We call ahead midday for reservations.
As for how your wife should survive this trip (I am the wife part here) - be sure to plan some things you both want to do, and to do some things you haven't planned. We really enjoy finding farmer's markets and local foods. Ever since the trip to Kentucky, I like to see what good places there are to buy bourbon :)