Cast iron is usually cheaper than cast steel because of the lower material, energy, and labor costs needed to produce a final product. Raw steel is more expensive to buy and requires more time and attention to shape. A big advantage of carbon steel over cast iron is that carbon steel pans heat up much faster. And because it's more conductive than cast iron, it heats more evenly and has fewer hot spots.
But even with that, it's still capable of reaching temperatures high enough to sear a steak nicely, and it can also be used on the stove and in the oven.