I believe that their is a limit for how much they will reimburse, $600 if I remember correctly. The total cost of the flights would be about $6000 for myself and my two co-founders as well.
If would be nice if there was more time between knowing you've been invited for an interview (April 7th) and traveling for the interview (April 23-28th). Since that's less than a month's notice, it means that airfare will be at it's highest.
