I have posted this before and dont know why the deal is expired , as the price promise doesn't expire, scroll down to article 26 on link
EasyJet give a price promise on online bookings, if the same flight becomes cheaper they will refund the difference via a credit note to be used within 6 months of issue. Though to get it you have to phone them rather than via email, letter, fax etc
Article 26 Price Promise
26.1 If You have, or the Booker on Your behalf has, made a Booking directly through the Website and You, or the Booker, subsequently find that lower fares (when taken together with all applicable fees and charges) for the same easyJet Flight have become available, You will be refunded the difference as a credit voucher against future Flights on easyJet. The only exception to this “price promise” is if the lower fares have been offered as part of a promotional offer that is launched after You have purchased the Flight. For the avoidance of doubt, this Article 26 will not apply to any Booking made on Your behalf by any licensed third party booking systems (e.g.: travel agents, screen scrapers) or through easyJet’s Call Centre.
26.2 Each Flight will be treated separately. This credit voucher will be valid for use against Bookings made within 6 months from the date of issue of the credit voucher. The credit voucher will expire at midnight on the expiry date and the validity of the credit voucher cannot be extended.
26.3 To qualify for a refund, the lower fare must still be available for sale at the time the claim is made to Our Customer Service Team and must be for the same date, destination and Flight number as in the Booking made.
26.4 If Your “price promise” request is in respect of a Booking that has been subject to a "Flight Transfer" or a "Name Change" request (see Article 8 (Name Changes) and Article 9 (Flight Transfers and Flexible Fares (“easyJet Flexi”)) then easyJet will only consider the total fare (including all applicable fees and charges) in the original Booking as the reference point for the “price compare”, not the sum of the all inclusive fare paid in the initial Booking plus the additional fees and charges incurred as a result of the name change or Flight transfer. All transfer fees and name change fees are non-refundable.
26.5 Claims made in relation to this “price promise” must be made via telephone to Our Customer Service Team. Claims made by fax, letter or email will not be accepted
I have just used this, bit of a slog as has to be done on phone and i'd also suggest you have website open at same time to ensure all done right as its an overseas call centre.
So far my price claims have got myself and the wife and 2 kids to Jersey , and also me n the Mrs to Nice.