Congress 'whacked' the budget by 1.5 billion dollars. = Congress 'whacked' 1.5 billion dollars from the budget.
Their priorities are (all) 'out of whack'. [=they do not understand what things are actually important]
I paid 'top whack' [=('US') 'top dollar'] for these items. [=I paid the highest amount possible]
(..) He beat them to the punch. Get the bank empIoyee fiIes and run down the prints on a guy named Ipkiss. You figure it was an inside job? I need some prints to Iock this whack job up tiII doomsday. grand... to whoever finds that green bastard before the cops. every Iow Iife in this town. Understand? (..)1994 The Mask