I think you'll find most of the YCs on LI go back to the Golden Age and there will be an initiation fee, plus annual membership
fee, plus referral by two members, with some sort of probie or junior arrangements. Membership
has been down in recent years with the economy. IIRC the Kinckerbocker in Port Washington
shut down two years ago. Most are social clubs, country clubs, beach clubs, not just a place to keep or sail boats. And most will gladly give newcomers a tour, often have some type of guest program to meet the members, who in turn can invite you to come sailing on those weeknight, etc. races with them.
Needless to say if someone says "come out with us this weekend" and you spring for a basket of sandwiches and drinks, you're very likely to be invited back out and shared with others who need crew.
But as for price
...in order to keep their restaurants booked, many also require
the members to spend a fixed amount ($500? $1000?) per season in the restaurant, along with the other costs. If they didn't do it that way, they couldn't keep the food
services open. That's just the way it is.
So sailing lessons
, even basic + intermediate, six days between them, should still cost a whole lot less than a YC membership on LI. Even less than a "junior" or "associate" membership. You'll have to enquire to find out, because it is taboo to mention filthy things like prices on their web sites.