If the simulation procedurally generates reality in space and time dimensions within the frustum and occlusion/LOD levels of the observer then in principle it wouldn't need a cosmological amount of matter/energy to run the simulation. It would be like a sort of library of babel. Even our minds could be part of the procedural algorithm and free will be just an illusion, there would be no free choices to make, no randomness or chance. It would all follow the next step of the procedural generator. Even if we don't live in a simulation this could also be the case if the universe is deterministic.