If you like the Spirit flight option, you can save the carrier interface fee (up to $23 per person per flight segment) by going to the Spirit ticket counter at an airport they serve to purchase your ticket. This is the least expensive way to travel bar none. Whether flying Spirit is worth it is a question only you can answer but I find them to be perfectly adequate when I'm paying for a ticket. This is especially true if they have a non-stop flights that work for your schedule but I've also taken connecting flights without issues. You can always book a back up flight on Southwest or another preferred carrier. Just remember to cancel the flight if you don't need it so you can keep the value of the ticket as a credit for future travel.