There are only a handful of copies exist, possibly rarer than #4. In Sep 2004 a VG copy sold at auction for £806.
In the Spring 2010 Comic Book Postal Auctions sale, a VFN- copy (lovely!) fetched £1331! The Highest Graded copy so far sold.
Jun 2015: Comic Book Postal Auctions raised the bar yet again for achieving record prices. A VG copy described as 'Bright covers, 2 ins horizontal spine tear. Some back cover foxing spots' fetched £1459 (inc a 14% Buyer's Premium).