A king size bed is wider than a queen size bed. While a queen bed is about 60 inches wide, a king size bed is 76 inches wide. Both are 80 inches in length.
A California King bed is longer but less wide compared to a regular King size bed. The dimensions of a California King bed are 84" length and 72" wide.
edit Video explaining the differences
This video explains the different sizes of beds and mattresses:
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:
"King Size vs Queen Bed." Diffen.com. Diffen LLC, n.d. Web. 24 Jul 2014. < http://www.diffen.com/difference/King_Size_vs_Queen_Bed >