Basic fares for transatlantic WOW air flights are usually really low an include only a flight ticket and one small personal bag with dimensions 42x32x25cm and weight up to 10 kg. You need to pay extra for everything else: a normal size carry-on, checked baggage, seat reservation etc. Note that there is also no meal service unless you book Wow Premium fare, pre-order meal or buy snacks on board.
Airline fares will keep rising the closer you get to departure, but there is a sweet spot when the airlines begin to either lower or increase fares based on demand. Don’t wait until the last second but don’t book far, far in advance either. The best time to book your flight is around 6–8 weeks before your departure, or around three months before if you are going to your destination during their peak season.