The place in the Cloisters is a small museum run cafe -- three sandwich choices, excellent brownies, coffee, soda, etc. in one of the most beautiful settings imaginable.
Near the Cloisters, in Fort Tryon Park, is the New Leaf Cafe. It is pricey and has a reputation for average food. I think you can find older threads here. Weekend brunch is $18 for coffee and an omlette -- a mimosa would bring your brunch up to $25 per person.