or is there another way to order anything he offers
Secondary market (eBay or private sale). You've just seen the aftermarket price.
Rainman is not a new artist. His company
Elfdoll has been highly regarded in the BJD (ball jointed doll) arena for a long, long time. Nude articulated blank bodies in the BJD realm, which are similar in scale to Sideshow's PF statues, can sell for $300 - 400. So Rainman's established price for complete 1:6 figures is not exorbitant in the context of his other work.
When you try to purchase something from Rainman for your collection of high-end collectibles, it's probably good for your sanity not to compare the cost to, say, a retail release from Hot Toys. Think of it this way: all you're trying to do is obtain one of a signed limited
fine art edition from a known artist whose 1:6 works are always limited to 15 or 20, usually with half that release available only to domestic (Korean) art collectors. The frame of reference is really not "collectibles" but other fine art markets -- photographs, lithographs, bronze sculpture and the like. In Korea, figure art is commonly displayed in and sold through art galleries, not stores, and its value is tied directly to the gallery's credibility. Nobody wants a counterfeit. So if you are lucky enough to have a Rainman figure, you just left collecting figures behind and started collecting artists. Congratulations, big spender.
The American seller in question may have been an art speculator, or may have sold due to hardship, or perhaps in order to buy some other high-end figure. We have no way of knowing. As long as the figure is genuine, aftermarket prices enhance the artist's reputation just as in other fine art fields. I doubt that Rainman worries too much about it. You might worry, however, because it will eventually drive his own prices up. But then, it will also raise the resale value of your Rainman original, too.
I was very surprised to learn that
any Chaplin v2 figures were sold in America though, as I'd believed that release was without fanfare. I'd thought they were all sold privately. I'm wondering if that's why Zuno asked who the seller is.