Trinisphere + Evoke

[Barook]

Let's say there's a Trinisphere in play and I want to evoke a Shriekmaw into play - how much would I have to pay?

:1::b:, :2::b: or :4::b: (:1::b: + :3:)?

I think I'll have to pay :4::b:, but I'm not sure.

[diffy]

502.74. Evoke

502.74a Evoke represents two abilities: a static ability that functions in any zone from which the card can be played, and a triggered ability that functions in play. "Evoke [cost]" means "You may play this card by paying [cost] rather than paying its mana cost" and "When this permanent comes into play, if its evoke cost was paid, its controller sacrifices it." Paying a card's evoke cost follows the rules for paying alternative costs in rules 409.1b and 409.1fh.


So basically as Evoke is an alternative casting cost, you'd have to pay 3 mana for your spell and therefore :2: :b:, someone correct me if I'm wrong though.
(Trinisphere checks upon casting and sees that you only paid :1: :b: which is less than 3 so the cost is upped to :2: :b:)
(Alegory to Force of Will which costs :3: under Trinisphere)

[TeKo]

:2: :b:

:1: :b: + :1: for Trinisphere.