Sorry for late reply, I have been out of wireless reach in Wales.
As with everything it depends on condition. ICERCs have a habit of the jelly yellowing which is unavoidable. Value is obviously less for a badly yellowed one. It's an uncommon model but not that rare, saw one on eBay a couple of weeks ago which didn't fetch that much, around £50 I seem to remember. PM me if you want to sell!