each unit being approximately 1000SF? area is bay ridge, brooklyn.

This is almost like asking how much it would cost to construct the Hoover Dam on the Hudson.

I'm exaggerating, but it's just too complicated for any online site. Start talking to some builders, and the zoning board/building inspector in Bay Ridge. Actually zoning first.

We can't answer that here, too complicated. To many variables. Definitely need to talk to zoning and permitting so to get guidance. Go from there.

I agree with joypulv and ma0641. Too many unknowns.

Its like asking I want a nice car.. how much will it cost. I can think of $30,000 "nice cars" and $1.9 million dollar "nice cars"

Pubic housing units won't be as expensive... OR as nice as Luxury apartments.

You need a LOT more info than you have provided. Even with VERY detailed plans and architectural drawings you have unexpected issues and cost overruns.