It’s already been said, but as far as I knew, when both are designed for entry levels and mass produced, they were similar in price as far as I knew. The thing is that steel bikes are becoming a rarity in the entry levels and a lot of the steel bikes around anymore are either:
A. Boutique-ish frame builders like Surly and Salsa that have cult-like followings among steel lovers who are willing to pay more.
B. Custom frames wherein the cost is not for the material, but the hours of work by a skilled worker in the first world as opposed the mass-produced bikes built by Chinese assembly line workers.

I can see how one might have gotten the impression that steel costs more.