Essence cost is shown by the number next to what I would call a "little blue shining stickfigure". But only in the spell list you get when "in game", not in the magic menu, which indeed is a problem when selecting the spell you want to research.

Also shown there is the mana required (number next to mana symbol), the "reach" of the spell, and something that looks like an hourglass (might be spell duration..)

This being said, you are thus right, and we need all the info concerning spells available before researching them.