S.H.
My son is in VPK. It is simply for four year olds to get them ready for kindergarten. It is FREE and not based on income at all. Preschools only have so many teachers, so each preschool can only accept a certain number of students, but other than that, I don't think it will be hard for you to find one. Just go check each one out and find one you are comfortable with. They have mandated standards to be able to even provide VPK, so your son will learn no matter where he goes.
I am already amazed at how much they are teaching my son! It is awesome that they offer this for free. You will still have to purchase supplies for your little student, so be ready for that, but it is minimal..like $40.
Good luck!