In reply to andrew_b_1975:
about £1 and preferably sold to me
seriously though, its highly dependent on what condition it's in:
pretty much new - under £250
Used a few times and not washed - under £200
Washed and well used - under £150
I based this on the retail of £300 but if you can find it cheaper you can adjust accordingly. Generally I would say that even if the jacket is new you should be able to take about 25% off the RRP. Having said this I got a shiny new Haglofs spitz jacket when it was new second hand for £150 (50% off).
If your haggling start well below what you want to pay for it.
Happy bartering