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Using this information, the average price is about US$670/pr which, using currency conversion, is £445/pr.
Typically a used item is worth about half of it original price, adjusted for condition and desirability. There are product that sell for as much today as they sold for new. However, such products demanding that high of price are rare.
I've not been able to determine when the speakers were made, but it seems they are about 15 years old. In speakers of this age, I would be concerned about the condition of the Surround, which in this context are the rubber/foam rings that connect the speaker cone to the frame.
Especially Foam Surrounds have a tendency to deteriorate over time, and in a sense disintegrate, crumble to dust. Gently rub your finger over the surround, it if is crumbly or gritty, then it is probably beginning to deteriorate. These Surrounds can be replaced at a pretty reasonable price. If you can find someone to do the work. There are YouTube videos demonstrating how Surround can be repaired.