It's probably just a fried logic board. When there was water on it, was it turned on? Sometimes when water hits our computers, if we turn it off and wait 48 hours with it upside down, a pb will just dry out. Try to buy a logic board from PB fix, eBay or even appeal to Apple to sell you a new one. I think the steep charge is that no one knows with out a diagnostic what exactly is fried on the machine. But, it is probably just the logic board and maybe battery contacts.