WANDF For Spirit Airlines Personal Item Bag 18x14x8 Travel Duffel Bag Underseat Foldable Carry-on Luggage for Women

$10 bag from amazon fits frontier perfectly.... https://www.amazon.com/WANDF-Foldable-Travel-Luggage-Resistant/dp/B07RWHFQKB/ref=sr_1_1_sspa?crid=2IDK13IDMUPG9&keywords=spirit+air+bag&qid=1687745813&sprefix=spirit+air+bag%2Caps%2C261&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1

I got this bag for $10 on Amazon it works