Given the number of copies of Walking Dead 100 I saw floating around Comic-Con, 383,612 copies of the comic were definitely not enough (especially when there were nine variants to collect). However, these books may not be as difficult to come by as one might expect.
On the first day of the con, the Wednesday of release, the books were going for $80 a set. each day, the price dropped. By the last day, the books were going for only $30 or so a set (I actually saw one stall selling the set for $25).
While we may be looking at the highest initial orders of any single issue since 1997, I think we may also be looking at something similar to the release of X-Men #1 (the highest selling comic of all time at 8 million sold). Have you tried to buy a copy of X-Men #1 lately? No? It is because everyone who wanted a copy was able to buy a copy without any hassle. There were so many printed, everyone got one. Now they are relegated to quarter bins (except for the one cover which combines al of the other covers. It goes for about a buck).
With the Walking Dead, the initial order was probably pretty close to the demand. Sure, there are some variant covers which are incredibly rare and fans will keep those prices high. but the average fan should not have any trouble finding a copy of the issue. And, anyone looking to score some quick cash by flipping the book on eBay is going to find it pretty difficult to find a buyer for anything more than cover price.
But, hey. We finally had a comic break the 380,000 mark! It has been too long. Now if we could only do that on a month to month basis. Now THAT would be something to celebrate!