I got 2 of them, each for $9.00. One to keep, one as a prize on this site once I figure out a cool enough contest.
What it is is Ultimate Spider-Man #54, except whenever they reference the movie Spider-Man they changed it to Arachnoman. And in the original #54 when Peter visits the set it shows the "real" Spidey and the "movie" Spidey side-by-side...in the Arachnoman variant the "movie" Spidey is replaced with Arachnoman, who is in a green & yellow suit. Other than that, some of the dialogue is different to make it make more sense.
I believe retailers had to order a certain number of the new Amazing Fantasy #1 to qualify to buy the Arachnoman variant, much like the Astonishing X-Men variant. Not sure how many.
I'm not entirely sure why they decided to do an Arachnoman variant. I read at first that it had something to do with being an alternative in case they could get some sort of permission to use the Spidey movie from Sony or whomever or the people involved. I noticed that Avi Arad's name is changed to Griffin Foster, so that's probably what it is.