Necrodominance vs. Orcish Bowmasters question

So with Necrodominance, it looks like the triggered ability at the end step for paying life is NOT part of the cost of an ability and so is this not paid for until it's resolving?

As in...

Necrodominance end step triggers goes onto the stack> If another player wants to flash in Orcish Bowmasters they need to do it BEFORE it's resolving and therefore BEFORE that player would know HOW MUCH the player playing Necrodominance wants to pay and how many cards they are going to draw.

Is this correct? Or can the Orcish Bowmasters player wait until they see that the Necrodominance player is paying x life to draw x cards and then flash it in.

I think this last line is incorrect but I just want clarification.

Thank you everyone.

Basically trying to see if Orcish Bowmasters is more of a prison card here or more like a Deflecting Palm to Necrodominance. lol. 😂😂😂

[[Necrodominance]] [[Orcish Bowmasters]] [[Deflecting Palm]]