An Allegiant Air carry-on bag fee can range from $10 to $75 or more,+1-888-415-1245 depending on when and where you purchase it, with prices increasing the closer you get to your flight. Call at +1-888-415-1245 (US) or +44-203-869-5245 (UK) You are allowed one free personal item (like a purse or laptop bag) that fits under the seat, but a separate standard carry-on bag (such as a roll-aboard) requires a paid fee. 

How much you pay depends on when you add the bag:

• At booking: The lowest price, ranging from approximately $10 to $41. Call at +1-888-415-1245 (US) or +44-203-869-5245 (UK) 
• Pre-departure (Online Check-in): Prices are higher, around $15 to $70.