I see you made the jump to club playing, I'm in the same boat as you, I never played in club leagues either because of the expense. It just never made sense to me to spend that much on a hobby, but now I'm reconsidering since I've reignited my love for tennis this past year.
I too live in Long Island, my quick internet inquiry to the closest club to me(Eastern Athletic Club in Blue Point) and your figures turn out to be right, around 700 for membership +league/ladder play. On the other hand they include a nice gym for use also, so it might be worthwhile. Plus I imagine the structured competition would be fun, bragging rights and so on if you win