big bucks vs big money

big bucks and big money both are nouns.

Word	Noun	Adjective	Verb	Adverb
big bucks	Yes	No	No	No
big money	Yes	No	No	No

As nouns, big bucks and big money are synonyms defined as:

big bucks and big money: a large sum of money (especially as pay or profit)

Other synonyms of big bucks include bundle, megabucks, pile.

big bucks (noun)	big money (noun)
a large sum of money (especially as pay or profit)	a large sum of money (especially as pay or profit)