code: def price_namespace( namespace_id, block_height, units ):
      
      price_table = get_epoch_namespace_prices( block_height, units )
      if price_table is None:
          return None
  
      if len(namespace_id) >= len(price_table) or len(namespace_id) == 0:
          return None
  
      return price_table[len(namespace_id)]
docs: Calculate the cost of a namespace.
      Returns the price on success
      Returns None if the namespace is invalid or if the units are invalid