I just booked a flight on spirit and found an 80% off coupon on their "deals" link. After searching all of the cheapest websites the exact flight I wanted was going to cost $220 for the round trip. I used the promo code "80pct" while booking it directly through the spirit website and got the same exact flight for $125. Not exactly 80% off but way cheaper than anywhere else and it seems to be site wide. No idea how long it will last but it's working right now, Good Luck!