I carry the Death Stroke Ultimate in my primary weapon bar; its tool tip states that it has a cost of 50 Ultimate. I usually carry either Soul Tether or Veil of Blade in my secondary; they have a cost of 150/200 respectively.
If, for example, Soul Tether is showing as fully charged I can assume that my Ultimate charge is at least 150; if I then use Death Stroke at a cost of 50 it might be reasonable to assume that my Ultimate charge is now 100 but my secondary Ultimate is always fully depleted (in effect Death Stroke has cost me 150/200 rather than 50). I assume that this is the way it's meant to work, but if so the term cost is perhaps not the most appropriate.
I am one of The Great Mediocracy, those whose role in life is to provide the baseline by which The Few deem themselves Great.