It seems even billionaires like Apollo Global Management co-founder Marc Rowan are having to adjust their price expectations amid an oversupply in the luxury residential market. The private equity mogul slashed the asking price of one of his co-op units at 927 Fifth Avenue by an additional $1 million, bringing it to $18.5 million, according to StreetEasy. It was first listed for sale last year for $22 million.