As far as the orginial 2500,- pounds go; not that shocking if you know how airfares work.
A flight only has a few deeply discounted eco fares. Than come the very discounted eco, discounted eco, normal eco, and up it goes. later on in the game, changes are realistic the discounted fares will have been gone, used up by tourists etc. The higher fares offer better options for changing dates, flights etc. but do come with a higher price tag. Not worth it for most tourists. So those are most likely available longer. Et voilà; when you ask for a quote for a flight that leaves within a relatively short time; the price will be a lot higher.
Actually, it's not uncommon for the highest fares of eco to be more expensive than the deepest discounted fares for business class. Which results in a nice financial lesson; always check all classes when the deepest discounted eco have been sold out.
Want to know how an airline names it's deepest discounted rates so you can see what you are quoted on their website? Google airlinename + farebuckets. That will give you a nice look over. For instance Continentals most discounted fares for eco are; W,E,S,T,N etc. They're mos expensive ones are amongst others; B, Y, M etc. Although, a B-fare with elite status can result in a direct upgrade to business on flights within the US if the R-bucket has availability. R stands for reward bookings with Continental, so the miles+money upgrade, uprgradable fares etc. Most discounted business/first fares for CO is Z.
To illustrate; I recently upgraded my CO eco ticket to CO BF. At that point out, hardly any seat was sold, so I got myself the Z fare for the Atlantic flights. BF tends to be sold mostly last minute, bought by folks travelling for work. As soon as I bought that Z-fare, that fare was sold out, and the BF price moved up to the first available fare. Of the 35 BF seats, only 2 or 3 were taken at that time. The price went up with a proper 30%. Haven't quoted it since then, but know it's higher up by now since the cabin is about half booked up.
Same thing will have applied to that 2500 pound quote. Cheapest fares were sold out, and thus quoted the "least expensive" still available fare in eco.