I just saw this when I checked the Frontier site. Book a round-trip (or two one-ways) by the end of the month and get 10,000 bonus miles. They do not count toward elite status but are certainly worthwhile in addition to the underlying mileage earning. Flights can be booked thru the end of the year.

https://www.flyfrontier.com/10k-special

There are plenty of $30-40 flights in September.

I am about 9k short of getting 50k status. While this is not a X3 elite miles bonus, it sure goes a long way to making one day turn around mileage runs worthwhile.