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 habit born of a long contemplation of eternity. - Forget about it, Vinnie. - Why? It's a simple hit. I'd love to smack Joey Zasa and then whack the fag. But it's impossible. He's always with people, in front of TV cameras in his own neighborhood. - It's not impossible. It'll work for us. - How? (..)1990 The Godfather Part III