Well, there is a Hampton in Santa Cruz that is cheaper but really, early September is still the high season for those coast resort communities. Monterey is always kind of pricey.
If you want to drop out of your preferred alliances to somethng a bit less expensive, try the Choice Hotels website. They have several properties in and around Monterey/Seaside in the $80-110 range for weekdays. Of course, a Clarion or Comfort Suites is not the ES but they are a lot cheaper.