I just order them off Amazon UK. Most of the releases are going for £9.98 which is just about under $20. They are pretty much Region 2's Criterion. Plenty of special features as well. Here's the link to their official website if you'd like:
http://eurekavideo.co.uk/moc.
I ordered the majority of what I own early on off
www.cd-wow.com. Prices used to be about $15 no tax/shipping. I think the prices have gone up since on that website.