What does the Rescue House Members casus belli cost?

prestige; the amount depends on the titles, claims and distance, worked out when you declare.

Casus belli · De jure

Rescue House Members

Rescue House Members is a casus belli in Crusader Kings III (de jure). If the attacker wins: Every … House member Imprisoned by the defender is released. If the defender wins: The attacker's House members remain Imprisoned by the defender. Declaring it costs prestige. The war goal is worth 75% war score. Patch 1.20.0.3, from game/common/casus_belli_types/05_fp3_wars.txt.

Quick answers (3)

What do you get for winning a Rescue House Members war in CK3?: Every … House member Imprisoned by the defender is released (patch 1.20.0.3).
What happens on a white peace?: The attacker's House members remain Imprisoned by the defender.
What does the Rescue House Members casus belli cost?: prestige; the amount depends on the titles, claims and distance, worked out when you declare.

How the war ends

Attacker wins

Every … House member Imprisoned by the defender is released.

White peace

The attacker's House members remain Imprisoned by the defender.

Defender wins

The attacker's House members remain Imprisoned by the defender.

If the war becomes invalid

The … has ended: the defender no longer has any imprisoned members of House …

Who can declare it

The game shows no text of its own for these conditions; the script is below.

Every de jure war (the group's allowed_for_character) (7 lines of game script)

herders_and_tributary_constraints = yes
pam_personal_pacifism_offensive_war_ban_trigger = yes
tgp_dynastic_cycle_offensive_wars_ban_trigger = yes
tgp_war_ban_all_ministers_trigger = yes
NOT = {
	government_has_flag = government_is_theocracy
}

As written in game/common/casus_belli_groups/00_casus_belli_groups.txt.

Attacker (allowed_for_character) (8 lines of game script)

is_house_head = yes
OR = {
	government_has_flag = government_is_clan
	has_perk = thicker_than_water_perk
}
NOT = {
	government_has_flag = government_is_landless_adventurer
}

As written in game/common/casus_belli_types/05_fp3_wars.txt.

Defender (allowed_against_character) (7 lines of game script)

any_prisoner = {
	house ?= {
		any_house_unity_member = {
			this = scope:attacker
		}
	}
}

As written in game/common/casus_belli_types/05_fp3_wars.txt.

Cost to declare

Costs prestige. The amount is worked out when you declare (by the titles targeted, claims, distance and more), so the script is shown as written:

Cost (8 lines of game script)

prestige = {
	value = 0
	add = {
		value = minor_prestige_value
		desc = CB_BASE_COST
	}
	multiply = common_cb_prestige_cost_multiplier
}

As written in game/common/casus_belli_types/05_fp3_wars.txt.

Source: game/common/casus_belli_types/05_fp3_wars.txt and the English localisation, Crusader Kings III 1.20.0.3. “The attacker”, “the defender” stand where the game names the character; “…” marks other words it fills in during play.