If I have a Church of Sigmar and the opponent play an attachment on my unit he have to pay 1 or not?

If yes, what about an attachment with constant effect (like Branded by Khorne), he have to pay 1 only when he plays it?

What about an attachment with not constant effect (like Bloodboil Fever), he have to pay 1 each time he trigger the action?

Thanks in advance

He needs to pay an additional resource to target your units. This includes playing an attachment on one of your units since it says "attach to a target unit". He doesn't have to pay an additional resource to trigger an attachment's effect unless that effect explicitly targets a unit you control. So for Branded by Khorne and Bloodboil Fever, it's just the one additional resource when the card is played.

Kingdom. Opponents cannot target your units with card effects unless they pay an additional 1 resource per effect.

Playing an attachment is a card effect? What is considered a card effect?

I found this: 

Card Effects (v1.4)
Some cards reference card effects. Card
effects is a game term that includes
Actions, Forced Effects, Constant
Effects, and Keywords.

I think that when I play an attachment, I have to solve the constant effect "attach to a target unit" and then pay 1. I was right?

 You pay all costs before you carry out a card effect.

 GAC, i was asking if it is correct to consider "attach to target unit" as a constant effect :)

Yeah, its a constant effect that continuously targets the unit.  If that unit ever becomes an invalid target for the attachment, it is discarded immediately.

 Humm, i'm kinda new to this game…

You only have to pay extra to target the unit the first time.  After that, it just stays on the unit unless the unit becomes an invalid target (i.e. it gets turned into a development) and you don't pay every round.