Hi
I guess you mean the 2.8 ?
I've got one and it's great but your DOP is limited wide open. I'd say anywhere between £1200 to £2000 depending on condition.
Mine looks like it's been dragged and run over by a tank, but optically it's perfect. I'd like a nice shiny one, just cos I'd feel happier.
It's heavy but balances nicely. The longer lenses get really heavy and impractical for transport overseas, also then you need IS.
Price wise I think the 300 f4 is a nice compromise.
John