I don’t have any specific information regarding scholarships but I would think you could start talking to the schools you are interested in and see what they can offer you. Many schools will work with you regarding tuition-not all- but maybe that will narrow it down for you, as well.
$20k/each for 3 children sounds like something you can negotiate down from, even at good schools.
+1.
In Lakewood, many solid schools charge in the range of $4,000 per kid. In Brooklyn, I think it may be a little more, but I don't think anyone actually pays $20,000. Many schools write the equivalent of an MSRP, but the real price is half that, or even less.
I think schools may be even more willing to lower the rate if the child is coming from public school, because they are vested in giving a Jewish education to every Jewish child. I think this would be the case even for middle-class families, not just to very low income families.