Incantatrix or Anima mage can apply the metamagic for free; a Greater Rod could do the same, though it would be prohibitively expensive.
Greater Rod of Twinning?
What book has greater rod of twinning?
Metamagic rods are: Chain, Empower, Energy Affinity (Acid, Cold, Fire, Electricity), Enlarge, Extend, Maximize, Quicken, Reach, Sculpt, Silent
Then Sudden Empower, Energy affinity (Acid, Cold, Fire, Electricity), Extend, Maximize, Quicken, Silent, Still, Widen
There is no Rod of/sudden Twin That I know about. Where did you find this?
Also, Incantatrix:10 -1 level metamagic I got that. Anima mage, I have no idea what you are talking about. How could an Anima mage cast a Twin Wish?
I mean, Incanatrix -1, Dweomerkeeper -1, Easy Metamagic -1, But then what? Ultimate magus won't help you. He can't affect 9th level spells. Hrm.... I suppose arcane thesis: wish. We're still talking what? 24th level wizard, minimum? Plus, you might run into a DM who rules that if one of those metamagic feat cost reducers says, "CANNOT GO BELOW +1", then he won't let you get to +0 cost on twin no matter what.
I suppose you could use alternative source spell from dragon magazine to make it a Divine Wish then use Divine Metamagic and burn 5 turn undead attempts. I have no idea who'd go through that much effort, but it's possible.
Just curious mind you. Don't really care one way or the other.