Searching our Desert Area Multiple Listing Service, I found 9 rentals that meet your criteria of being unfurnished and having a casita in the 3 locations you like.
The price range is from $2500 per month and up.
The link below shows the 2 lowest priced rentals. If I can help in any other way, please contact me.
Carolyn Voet (Lic: 01505751)
Windermere Real Estate (Lic:)
73-993 Highway 111
Palm Desert, CA 92260
View Listings link will be available for 90 days. If you do not see a link, copy this text to the address line in your browser:
http://www.trulia.com (Rentals Section)
http://www.zillow.com (Rentals Section)
http://www.realtor.com (Rentals Section)
Between all of those, you will get a very clear picture if you can find what you are looking for. Good luck!