When selling anything you have to weigh up what you want, a quick sale but maybe at a lower price than you would ideally like, eBay provides this, 7 day auction sale done, lots of potential buyers, UK wide, but being an auction unless someone meets your idea of a decent price it will go unsold, otherwise sale is confirmed at the end of auction.
Or try to sell privately, by advertising in Auto Trader etc where it will cost especially if you want a colour photo and Internet exposure to get UK wide coverage and not local area, no guarantees on sale during your 3 week advertising period, maybe a few potential buyers and all the while you are paying insurance, road tax and MOT are getting shorter but ultimately if you wait long enough a sale will come at a better price but with more outlay.
As with anything, its not worth more than someone is willing to pay.
Aaron.