For size comparison of the Raptor engine. Left the Raptor as used on the booster in the picture above. Right the vacuum version that will be used on the orbital Starship.
Everything designed not just for raw power but for low cost. Presently a Raptor engine may be in the cost range of $500,000 but target price at mass production in the new factory is ~$250.000.
A whole stack of Starship booster and orbital Starship will cost way less to build than a single main engine for SLS, which is $100 million. Though to be fair Raptor price is cost, SLS engine is what NASA pays to Aerojet Rocketdyne for one. After NASA has paid AR for building the factory.