Your budget is the limiting factor. In new, there is virtually nothing in that price range that will equal they quality of the Xarus 5000, which are normally £450/
pr.
In used, I'm sure there are used speakers that are fantastic for the money. All you have to do is find them. With used speakers you are at the mercy of the market, and at the mercy of your own ability to know what speakers are worth buying and which are not. That typically comes from years of experience with a variety of speakers. Also, you are somewhat at the mercy of the seller, and the degree to which you can trust him to accurately represent the speakers under consideration.
So, yes absolutely there are outstanding bargains in used equipment ... all you have to do is find them, and know them when you see them.
I would suggest checking this Forums For Sale section. It is pretty closely monitored, and generally trust worthy.
Ebay is a good source, and within limits, Ebay does give you a degree of protection.
The advantage of the Xarus is that it is a lot of good speaker for an insanely low price. The disadvantage is that there is no matching Center speaker.
It might also help to know what speakers you have now.
Steve/bluewizard