Ki is 1 per level, same as Sorcery Points, but come back on a short rest, so could be 1 to 1, 1/2 or 1/3, etc, depending on how many short rests you're having.
You can turn 2 SP into a 1st level slot, so 1 Ki could be worth as little as 1/6 of a 1st level slot, which honestly could be the case...