Short break to London with a direct flight from Athens from 57,58 euros with the "official" student carrier, www.ryanair.com
To and from Stansted airport
For 0 euros check couchsurfing.org
Also check airbnb.com it might get much cheaper and more cozy from hostels and hotels. (I have a gift for you there)
-Plan wise your trip to and from Stansted airport, the airport is quite big and you might need to take an internal train to reach your terminal so make sure you won't miss your flight or your bus.
-Book your trip to and from the airport early enough to take advantage of the early booking offers especially from www.easybus.co.uk
-Don't forget to check in online and print your tickets. You can also use ryanair's mobile app for check in.
-Always double check while crossing the streets.
-Before deciding to exchange money, check your bank's exchange rate usually it's cheaper. The fee for withdrawing money is the same as it's in your country when you withdraw money from a different bank.
-Time flies, prices go high!
-Don't forget your sunglasses