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]
(..) -I see what you're doing . -What are we doing? If you're gonna steal from Terry Benedict, you better goddamn know. This used to be civilized . You'd hit a guy, he'd whack you. But Benedict.... At the end of it, he'd better not know you're involved . Because he'll kill you, (..)2001 Ocean's Eleven