I hired a Senaca for 100 hrs from Air Dessert Pacific, San Demas near LA. The cost was around $110/hr. The A/C look old and tatty but I had no problems.
Generally they prefer people to stay within the three or four state radius but you can arrange with them to allow you to go further afield. When I was there someone took a single to the east coast and back.
ADP advertise in all the mags I believe. The staff are friendly.
ADP tel:+(1)-909-596-6059
Web:
www.airdesertpacific.com
regards