All depends on a variety of things: Where it is being sold (ebay, fb or forums), Condition, Grade and item location.
Loose ungraded £280-400 if Euro based. £400-500 is America/AUS based. US folks tend to pay more, but seem to not bid on the Euro ones.
UKG graded £350-450 depending on grade (£350-400 for a 75, 400-425 ish for 80 and can pick up 85s for £450). Add about £30-50 if seller based in America and on ebay.
AFA Graded - similar to above but about £25 more... unless, again, seller on ebay based in America/Aus then you would be looking around £500-650 ish.
90s are a bit all over the place re: pricing.
So to sum up, if buying: purchase from a Euro based seller on ebay. If selling: try and hit the US market - so don't ebay it unless you are based in America or Aus, if youre euro based hit the forums or facebook looking for the US folks.
Hope that helps.