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]
(..) a marriage for years, but you were happy as long as I kept my mouth shut. Well, guess what. I've changed. And the new me whacks off when he feels horny... 'cause you're obviously not going to help me out in that department. I see. You think you're the only one who's sexually frustrated. (..)1999 American Beauty