In "The Last Line", the special setup indicates that 3 reinforcement waves are to be set where the "combined deployment cost is between 6 to 10"

The Imperial player has "Bounty" Reward card and "Hired Help" Agenda card reducing the deployment cost by 3 "When you deploy a Hunter"

The question is, do these reduction apply to the reinforcement waves? I'm guessing not since the reduction only applies when the group is deployed, and not when the reinforcement wave being created?

No. When you're choosing the waves, you're not deploying, and thus no cost reduction.

That's what I thought! Thanks