Great fun to collect and you can spend many hours trying to figure out the order of publishing, the reprints and different editions, the cover price dropping to a shilling from 1/3d and the original British editions. Classics Illustrated began in America and ten years later Strato Publishing based in Oadby Leicestershire began reprinting them for the UK market.
Confusion arises from the fact that not all US editions were printed, four numbers were used twice and the published order differed from the numerical order on the cover.
There were 13 original British issues not reprinted in America and this is where the big values can be found. For example Through The Looking Glass #147 line drawn cover about £100-£150, The Aeneid #161 with painted cover can fetch £200-£350, Dr. No #158A painted cover £250-£450, A Christmas Carol #53 painted cover anything from £300-£450 and Mr. Midshipman Easy #74 2 shillings cover price and painted cover I have seen listed at over £1,000 on eBay UK. But whether it sold or not I couldn't say. These values are for first printings and in very nice shape condition. Most other issues generally appear on lists and on auction sites in G to VG mid grades and sell in the £5-£15 range.
For more information I would have no hesitation in recommending Bryon Whitworth's Complete Identification Guide. Limited to 200 copies, it was published in 2007 and is a magnificent piece a work, stuffed with illustrations and information. It pops up on eBay UK occasionally. Grab it!
With thanks to the very excellent Book Palace for some cover illustrations. Go visit their amazing web-site www.bookpalace.com.
Note: some PR issues may have no value. Selected issues in FN, VF or VF/NM may not exist in some titles.