Empathy is inexpensive and brings surprising benefits. It takes a little bit of practice and intent. Mainly, it involves stating the obvious assumption about the other person's experience and desires. Offer things you think they'd want and that you'd be willing to give. Let them agree or correct you. This creates a good context in which high-value trades can occur, without needing an conscious, overriding, selfish goal to guide you from the start.
In that case, I don't agree that the thing you're claiming has low costs. As Raemon says in another comment this type of intuition only comes easily to certain people. If you're trying to lump together the many skills I just pointed to, some are easy for others and some harder.
If however, the thing you're talking about is the skill of checking in to see if you understand another person, then I would refer to that as active listening.
Of course, you're right. This is more a reminder to myself and others who experience empathy as inexpensive.
Though empathy is cheap, there is a small barrier, a trivial inconvenience, a non-zero cost to activating it. I too often neglect it out of sheer laziness or forgetfulness. It's so cheap and makes things so much better that I'd prefer to remember and use it in all conversations, if possible.
Empathy isn't like brushing your teeth. It's more like berry picking. Evolution built you to do it, you get better with practice, and it gives immediate positive feedback. Nevertheless, due to a variety of factors, it is a sorely neglected practice, even when the bushes are growing in the alley behind your house.