from typing import Dict


def get_noise_exposure_index(
    noises: Dict[int, float],
    db_costs: Dict[int, float]
) -> float:
    """Returns the total noise cost (i.e. noise exposure index) based on exposures to different noise levels
    and db_costs.
    """
    if not noises:
        return 0.0
    else:
        return round(sum([db_costs[db] * length for db, length in noises.items()]), 2)