One of the reasons that NYC and its suburbs have a higher cost of living than upstate New York is because they have higher county taxes. They have higher county taxes because each county has to pay for it's own Medicaid. The larger counties have more poor people in them. New York State is notorious for having horribly inefficient Medicaid system.

Also, just because the U.S birth rate is declining doesn't mean that it will eventually have a negative growth rate. The U.S population is still growing, but just not as rapidly.

There are countries that are experiencing negative growth rates right now; Russia is one of them.