It varies quite a lot and some people ask rediculous prices.
Here in Holland a medium condition and relative complete wd16H may go for anything between 4 to 5.000 euro. Bikes in Germany are usually more expensive.
I'd expect the price to be a bit lower (in pounds) in Britain.
I have seen a Belgian (completely wrong) restored one asking 13.500 euro and a Frenchman with a very good restored one for 25.000 euro.
I do not believe they will ever get that money but there are lunatics with to much money and no knowledge (or care).
These silly prices do however have a negative effect on other sales as people start expecting more for their bikes.
Good luck in the search and let me know if you find one?