By Michael Tedder Let’s just hope the airline is cool with that. If you want to know how much it costs to take a Southwest flight, there’s only one way to find out. Southwest doesn’t let third party apps like Google Flights, Expedia, Kayak or other travel agencies share or sell its fares. While it’s a bit more aggressive than most, Southwest isn’t alone in trying to get customers to shop direct, as many airlines will offer discounts if you book through their site. There’s several reasons why airlines prefer you shop through them. They have to pay a referral fee for a website like Kayak, and wh…