Before I check if I've quested successfully, suppose I exhaust Radagast's Staff, and then want to play a Tactics Creature via Hirgon. His response says, "...reducing its cost by 1 (to a minimum of 1)..."

If the ally costs 3, I assume it now costs 1. (Staff is -2, and Hirgon can't reduce it further).

But what if the ally costs 2 (or 1). Would it cost 0 because Hirgon can't reduce it further? Or still 1?

The real question is, does Hirgon still pay 1 for a 0-cost ally? So even without Radagast's Staff, the only eligible Tactic ally (as of now) is Dunedain Hunter.

58 minutes ago, JYoder said:

The real question is, does Hirgon still pay 1 for a 0-cost ally? So even without Radagast's Staff, the only eligible Tactic ally (as of now) is Dunedain Hunter.

Hirgon says "reduce to cost to play it by 1" so I assume that if the cost is already 0 it should stay that way.

58 minutes ago, JYoder said:

If the ally costs 3, I assume it now costs 1. (Staff is -2, and Hirgon can't reduce it further).

But what if the ally costs 2 (or 1). Would it cost 0 because Hirgon can't reduce it further? Or still 1?

If I am not mistaken there are precedents indicating that you can choose to your adanvate the order in which you apply the discounts (like applying first Hirgon and afterwards SpTheoden not already triggered to play for free a 2 cost Rohan Tactics ally) so with Hirgon + an already triggered Staff you should be able to play for 0 a 3 cost Tactics Creature ally.

Some of the reference rulings on stacked cost reduction: