The dimensions of a King size and a California King Size bed - also known as Cal King - are different. A standard (Eastern) King size bed is 76" wide and 80" long; while a California King size bed is 72" wide and 84" long.
Another difference is that California has more stringent flame retardant requirements.
California King size bed is also known as Western King, Cal King, WC King or West Coast King.
Standard king size and Cal King are among the largest standard sized beds. The next biggest is a queen size bed.
edit Video explaining all bed sizes
Prices varies by the distributor, the type of mattress (spring, memory foam etc) used, accessories etc. Current prices for a few products are available on Amazon.com:
"California King Size vs King Size." Diffen.com. Diffen LLC, n.d. Web. 25 Jul 2014. < http://www.diffen.com/difference/California_King_Size_vs_King_Size >