In terms of full-service Marriotts and Rens, it's hard to beat Phoenix in the dead of summer. I've gotten as low as $59 at the Scottsdale Renaissance. (Though I actually book the Tucson suite with the margarita package just to bump up the rate to $99 and get more points...nothing the company would red-flag on my expense report!)

You can even get in Camelback for under $100, though it's hard to do.