Rakdos, the Muscle / Cost Reduction | tcgmode

I was wondering, if I had exiled \[\[Rakdos, Lord of Riots\]\] (for example) with \[\[Rakdos, the Muscle\]\], and I had \[\[Herald of Slaanesh\]\] or another similar cost reduction permanent out on my battlefield during, would casting Lord of Riots from exile now cost two mana of any colour, or s...