import geopandas as gpd
import pandas as pd
import numpy as np

county = gpd.read_file('/home/bera/GIS/data/test/kommun.shp')
prices = gpd.read_file('/home/bera/GIS/data/test/housing_prices.shp')

price_column = 'price'
zip_area_id_column = 'county_id'

inter = gpd.overlay(county,prices)
inter['area'] = inter.area

wm = lambda x: np.average(x, weights=inter.loc[x.index, "area"])
f = {price_column: {'weighted_mean' : wm} }
newdf = inter.groupby(zip_area_id_column).agg(f)
newdf.columns = newdf.columns.droplevel()