Really hard to value, loads of money 18 months ago or so but things (private sales at least) seem to be selling a lot slower recently.
Theres a pretty one on Ebay right now, keep your eye on it and it'll give you a general idea of what people are currently willing to pay which if you're buying is far more use than knowing what someone is willing to take.

Now though (i.e. winter) is a good time to buy as prices start to creep up in spring...
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