Technically, the ones from Amazon shouldn't be DRM-ed, since Subterranean's listings all say "Simultaneous Device Usage: Unlimited", which is the code phrase for DRM-free.
However, they are geo-restricted and may not be available outside the US.
At Baen, if you're willing to pick up several other authors at the same time, Dreadful Skin
drops to $4 when you buy it bundled with 5 other books for $24
, available worldwide.
I wish Subterranean would put more of their stuff up on Webscriptions. I really like their catalogue but am not particularly interested in acquiring limited-edition hardcovers for most titles and I'd be perfectly happy to get them as e-books MultiFormat, DRM-free, and most importantly, openly sold to my country.