I think I have a copy of every Series E lens that was made by Nikon. Inexpensive and a lot of plastic and unless you have some very specific reason for wanting the "true" Ai-S lens, save your money, get the Series E, try it, see how it works out, if it doesn't sell it and get the other.
Honestly, in my case, I have more worries about ME getting the shot in focus than the lens resolving the image on the film. With all my manual focus lenses, expensive or cheap, when I am able to nail the focus.......the picture is sharp enough. Composition and the character of the photograph is going to make the picture. I can't really say I have any bad copies of any Nikon lens so far.
I can back up my above statement too.....routinely I use a AF teleconverter on my F4S with mostly MF prime lenses. When I do, even chasing after the soon to be 4 year old girl, I am able to nail the shot with perfect focus.......not exactly 100% with the FA or the FE unless everyone is standing still and posing....for a long time....which they hate.
I got my EX or EX+ Series E 28mm from KEH about 2 years ago, it still looks like nobody ever used the thing (like most of my Series E primes). However, great glass is great glass and that 2.8Ai-S is noted as one of Nikon's best, so if you can swing it, get it. You will always be able to get your money back with great glass if it doesn't work out. And yes, I too have been looking and scratching my head over this too......I really want one of the Ai-S lenses too, I just have to much other equipment I need to get instead.