It depends from Situtation to Situation, and club to club. A lot of factors go into the price calculation. Seating capacity, total capacity, heating, roof, the city you are in, the attraction level of the city etc. But my approximate guess will be 10 Mil + 1 Mill per 1000 seats for stadiums of capacities over 20000. The smaller 5000 ( 2000 sitting ) stadiums cost around 3-8 Million.
These are just number i've giving you based on what I and other people around the forum have paid.