The cost reduction applies only to generic mana in the total cost of spells you cast with the permission granted by Urianger Augurelt's last ability.

To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as a flashback cost), add any cost increases (such as kicker costs), then apply any cost reductions (such as that of Urianger Augurelt's last ability). The mana value of the spell is determined by only its mana cost, no matter what the total cost to cast that spell was.

Urianger Augurelt's first ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered or otherwise leaves the stack. (Playing a land doesn't use the stack.)

If one of the exiled cards is a land card, you may play it only if you have an available land play remaining this turn.

You pay all costs and follow all timing rules for cards played with the permission granted by Urianger Augurelt's last ability.