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.
You're not crazy for thinking that a flight price has changed after searching it a few times in your web browser. Based on the cookies in your browser, flight prices do increase when a particular route is repeatedly searched, as the site wants to scare you into booking the flight quickly before prices get even higher. Always search for flights in incognito or private browsing mode to see the lowest prices.