Lila’s middle ability doesn’t change when you may cast those spells. You still pay all costs for those spells as well.

Common cards have black expansion symbols. Cards from before Exodus™ don’t have expansion symbols; their rarities can be found on their Gatherer entries. (Cards with the land rarity, including basic lands, also have black expansion symbols, but Lila doesn’t let you play lands, so this hardly seems worth mentioning. Oh, sorry.)