Iceland’s Wow Air just launched some incredibly inexpensive flights from Boston and Washington, DC to London and Copenhagen, routed through Reykjavik, in what may mark the kick-off of a transatlantic budget airline boom that many in the airline industry have long expected.

Wow joins Norwegian Air, Europe’s third-largest budget carrier, in offering cut-rate transatlantic flights. Industry giant Ryanair has said it would like to follow suit. New fuel-efficient planes like Boeing’s 787 Dreamliner and lower oil prices might make it a crowded field—if you can stomach the carbon footprint.

Wow will fly from Boston starting in March and from Baltimore-Washington International airport starting in June, with fares as cheap as $99 one-way to London and Copenhagen, including taxes. But good luck trying to keep your total costs under a C-note. Wow—whose corporate slogan in “cheap and cheeky”—is a budget airline, which means charging extra for absolutely everything, along with some other quirks:

Fees, fees, and more fees

If you pack a carryon that’s less than 11 lbs (5 kg) and you’re happy not having an assigned seat, you are good to go. Otherwise, break out the credit card; here are some of the fees you’ll face, as compiled by the travel site Jaunted:

Carry-on luggage 5-12 kg (11-26 lbs) = $38

First checked luggage <20 kg (44 lbs) = $67

Seat reservation, XL legroom = $24

Seat reservation, front of plane = $14

Seat reservation, middle of plane = $9

Seat reservation, back of plane = $3

Most of those prices are for paying online; if you book any other way it will cost more. Wow also charges for unaccompanied children—the chaperone fee is €55 ($69.50) per flight leg.

Prepare to book ahead—waaaaaaaay ahead

Those attention-grabbing $99 and $125 fares are only available if you book for travel that is many months away, despite the fact that the flights have been available for less than 24 hours. As of publication time, the site is only showing the lowest fares for routes like Boston-London beginning in September 2015.

Flying to Reyykjavik costs more than connecting through it

It costs as little as $99 to fly from Boston to London or Copenhagen, after a connection and short layover in Reykjavik—but $129 to fly just to Reykjavik. Sure, you could just carry on your luggage, disembark in Iceland, and not take the second flight, but make sure you didn’t book a round trip—airlines usually cancel the whole trip if you don’t fly every segment of a reservation.

Flying east is cheaper than flying west

A flight from Boston to London costs $99 if you travel on September 20, but it costs more than three times as much to return a week later.

Connecting flights might not be on Wow, exactly

Some flights between Reykjavik and London are operated by Air VIA, a Bulgarian charter airline that leases some of its planes to Wow.