As many as 3 million New Yorkers may be fraudulently reaping taxpayer-funded Medicaid and other public health insurance benefits at a potential cost of $20 billion a year, a staggering new study claims. About 5.5 million Empire State residents have incomes low enough to meet the standard eligibility limits for Medicaid or the Essential Plan, a related public health insurance program. But with expanded eligibility rules under Obamacare and an increased demand for a controversial homecare program, enrollment has swelled to 8.5 million, a potential surplus of 3 million.