Saheeli, the Gifted

The total cost to cast a spell is locked in before you pay that cost. For example, if you control three artifacts, including one you can sacrifice to add colorless mana , Saheeli's second ability will reduce the cost of a spell you cast by 3 generic mana . Then you can sacrifice the artifact when you activate mana abilities just before paying the cost, and it remains reduced by 3 generic mana .

While resolving Saheeli's third ability, each token copies exactly what was printed on the original artifact and nothing else (unless that artifact is copying something else or is a token; see below). It doesn't copy whether that artifact is tapped or untapped, whether it has any counters on it or Auras attached to it, or any non-copy effects that have changed its types, color, or so on.

To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions (such as that of Saheeli's second ability). The mana value of the spell remains unchanged, no matter what the total cost to cast it was.