A Frontier Airlines plane lands as a United Airlines plane prepares to take off at San Francisco International Airport. Credit: Tayfun Coskun/Anadolu/Getty Images With airfares projected to skyrocket due to rising oil prices, travelers are on the lookout for a great deal. And sure, those budget airline prices look tempting—but hang on, because there are a few things you need to consider before clicking "book." Setting aside the in-flight experience and looking purely at fare totals, flying a budget airline can seem like a fantastic deal. Don't let that lure you in, though. Low-cost carriers have to earn money too, and they often do so with significant add-on fees, which can drive that seemingly low price to new heights. Just look at Spirit Airlines as a prime example. The carrier revealed in its 2024 earnings report that its average fare revenue was $45.02 per ticket; however, it also reported earning an additional $63.44 in "non-ticket revenue," aka fees.…