I'm betting that #1 will go up before it goes down and I'll tell you why.
There's at least three more seasons of the show to come and it will keep going on if the ratings are solid.
There's at least another 100 issues in the monthly series. So, what's that, 8-9 years, minimum. Unless Kirkam wants to stop. But, from what I've read in the 'hacks' pages, that doesn't seem likely. Even then, if the book is selling 50,000 copies a month, someone else will take over.
Also, Kirkman didn't just create a story here, IMO, he created a "universe". There are so many stories that can be told. "The Walking Dead" is just one series in that universe.
I wouldn't be forking out $500 for a copy of #1 either - I paid $30 for mine - but $500 might not be a bad price now, we just don't know. That is what makes this hobby so interesting. To me at least.