product.rb

class Product
  def list_price=(price)
    write_price(:list_price, price)
  end

  def sales_price=(price)
    write_price(:sales_price, price)
  end
  
  private
  
  def write_price(attribute, raw)
    sanitizied = raw.to_s.gsub(/[^\d\.]/, '')
    write_attribute(attribute, sanitizied)
  end
end