It's a world where everything comes down to money.
Literal
All-things [subject-が] money's world [copula-だ].
A noun-predicate aphorism. 金の世の中 ('a world of money') asserts that money pervades all. The が marks 万事 as the subject of the copula — 'everything is (of) a money-world.' The rhetorical compression makes it read like a resigned observation about society.