There is a plan to divide NY, but hasn’t got much lift:
https://www.divideny.org/divide-new-york-plan.html
Won’t save a dime. Not workable. Creates more government positions (the “regional” governments) while retaining a state government as well. The three way split does not seem natural, and especially the “Montauk” region seems most unnatural - Nassau and Westchester are not naturally “together”, nor is Nassau & Rockland, nor Rockland & Westchester; and the interests of Suffolk county and Westchester & Rockland counties is about as far as you can get.
A two-way TOTAL division (two states) would be best.
The New York Metro area of New York City, with Long Island and Westchester county would be one new state. Everything north and west of Westchester county would be New York State. The agreement would keep New York City with ownership rights to its water system and zoning and development rights over the watershed from which the water is obtained.
Much less messy, much less complicated, clean and separate.