I've got boxes of them. They were such an important way to share ideas. They're mostly in the loft, not all though, some are still in the wild.
These are the first three pamphlets I found.
"A State of Siege Policing the coalfields in the first 6 weeks of the miners strike". Cost £2 in June 1984. 66 A5 pages, rather dense print, not many photos
"A Tax on Peace Conscientious Objectors & the Taxpayer" £1.50, no obvious date. 50 A5 pages, only 1 photo
"Without a Trace a forensics manual for you and me" £2 no date 32 A4 pages. This one's been dtp'd so a few graphics/photos.
e2a according to the site Cesare linked, 18,000 words of 10pt Courier is 32 A4 pages. The miners strike pamphlet is somewhat smaller than 10pt so 66xA5 is probably over 20k words. It's not an unusually thick or dense pamphlet though.