Who comes up with worth?

Who comes up with worth? Who estimates what the value of something should be? This 20 billion dollars, did that figure come from our Government or BP? I'd like to know exactly who it was that came up with that amount? Did anyone from the government arrive at that price or did it come from BP? I bet if you ask the people along the Gulf Coast what it should be they would probably tell you that the big banks got a lot more bail out then that! That's probably what it cost to bail out only just one bank.