The early issues are the most collectible, up to about #50 or so. These all pretty much suffer from staple rust and many only have the one staple holding it all together. Ask the vendor how bad the rust is! Issues after that seem to be less rusty-staple prone. To get absolutely clean copies is truly a wonder to behold.
Indeed a copy of issue #1 with very bad staple rust and with a taped spine sold for £31.90 on eBay UK in Mar 2008. It can be surface rust or practically disintegrating! Haven't seen what I would call a Very Fine #1 and definitely not seen a Very Fine/Near Mint #1.
There are at least 2 volumes of the Thriller Picture Library Index and a third is planned, compiled by David Ashford and Steve Holland, two very fine gentlemen. Stuffed full of detailed infornation on stories, characters and artists, these are required reading for any serious fans.
Note: some PR issues may have no value. Selected issues in FN, VF or VF/NM may not exist in some titles.