tee hee, I was wondering that too! I'm guessing they get scans from someone who has the book? And they translate off of them? Or they buy the book...but I don't think that's likely.
Well, scans are one option. Because some of the stories are in a magazine, you can get it there. Also, because Haruhi i so popular, some people have wrote out the entire volume (I've seen the raws for volume 1-9).
I think you can (order things from Japanese websites). Well, at least from certain ones. Also, there are some sites that sell things that are Japanese but have everything else (the text basically) in English (I think).
Suzumiya Haruhi no Bunretsu (Vol. 9) (2 copies) = 1,028 yen (~US$8.50)
Shipping to Continental U.S. = 3,300 yen (~US$27)
That shipping was harsh. I might look into another importer because of that... but I'm confident Amazon.co.jp will always be a viable option if nothing else pans out.
=Smidge=
It's about US$30. A good rule of thumb for putting yen into US$ is just divide by 100, but the actual yen value of one dollar has seem to be around 120 yen for the past year or so.