Unlike the other food items, all fruits require 5 units to research in Journey Mode.
All these fruits sell for 20 apiece, whether or not they have been crafted -- that is, juices, cocktails, and fruit salad all sell for 20 per fruit that went into them. The Hallow fruits have the same price despite giving a better buff.
While grapes in the real world are certainly fruits, in Terraria, Grapes do not fit into this grouping at all -- they drop from enemies instead of trees, and do not participate in the "Any Fruit" recipes. They do have a juice recipe, but both Grapes and Grape Juice give the more powerful buff Exquisitely Stuffed. They and their juice sell for twice the price of "regular" fruit and juice, and in Journey Mode, grapes require 10 units to research instead of 5.