Spirit provides one free personal item, but a carry on bag could cost anywhere between $15-35 at booking.

Carry on measurement

 22 x 18 x10 inches

Metric

56 x 46 x 25 cm

Cost

Depends on your flight. Cost calculator linked below.

https://www.spirit.com/OptionalServices

Personal item measurements

18 x 14 x 8 inches

Metric

45 x 35 x 20 cm