I was traveling around in the south west of the states with one more person for a month with a vague plan for the route (also to make sure you'll make it back to your plane in time) and a rental car. That was a lot of fun too. There's plenty of motels all over like in Australia and I haven't run into any mad people trying to annihalate us. Then again we probably stayed clear of bad neighborhoods (as I would in any country).
Vegas is fun and affordable (expecially if you don't gamble
) the Grand Canyon was amazing but there's a lot of nice places all over.
That was my experience, hope it's useful
added:
Oh, if you're a trekkie;
there is a Star Trek Hilton in Las Vegas. it just started up when I was there , so it must be even more cool now. Check for prices for more than one night they tend to be really affordable!