As said before, the days of buying directly from the studios is over and even when that was going on it was normally 1K - 5K plus posters you had to buy to get them. They also were not being sold for fractions of a dollar like the stone age NSS selling days, the studios were making money on these sales, think thousands here, not $500 gets you 1000 posters. There is not a title out there that would sell that kind of quantity anymore. While the hobby is still strong on the collectible side, the casual home theater, bedroom wall buyer base is probably a 1/3 of what it was 10 years ago or even 5 years ago for that matter.
Some of the smaller studios, if you catch them on a good day, might sell from time to time, but those are few and far between as well.
I am speaking to my pricing, but this holds water as a general rule, 90% of the new releases on ebay are priced below what you can buy them for on the "wholesale" market, so I really dont see the price gouging at all. The top 10-20 box office films a year you may have to pay what is considered retail unless you roll the dice and buy at auction and get your poster shipped to you in a triangle mailer or a wrapping paper core.
Even if you could still buy into a run, raise your hand if you want to gamble on 1000 pieces of a film that tanks and you have 975 of them left you cant get rid of.