They typically turn up on vg condition with rusty staples - especially the earlier ones. A few years ago some of the early Air Ace were discovered in a shop that had been closed up for many years that were in near perfect condition. They were rather expensive on Ebay UK.
However, these are eclipsed by another title, Commando, which is still in print many thousands of issues later. Early issues go for hundreds of pounds regardless of condition. They are no better or worse than the titles I have posted. But while I didnt mind paying as much a s £20 for an Air Ace in as-new condition, I would not pay £1000 for Commando #1!
From the internet - issues #1 and #2:
and a linky:
http://cloud-109.blogspot.com/2010/04/achtung-commando.html