Are you opposed to bootlegs? European Trash Cinema and some of the gray market places are good sources. Many bootlegs are crap, of course, but that's usually because that is the only existing version.
I understand why some people only want factory-sealed DVDs, but I DON'T get why people have a problem buying from a bootlegger, but don't have a problem paying the huge mark-up of Diabolik or some Amazon sellers. To me it's like the old days where I might rent a movie for $5-10 (the average price of bootlegs today and pretty close to what video rental fees once were adjusted to today's dollars) instead of buying it for $35 (which is what rare VHS back then or import DVDs todays often cost).
But pardon the loud scraping of my soapbox there--occasionally you can lucky and find factory-sealed DVDs of import titles at discount prices. I don't have a single source, but you might get lucky googling the title.