Turns out it's being (kind of) matched against the official price of $0.00 directly @
the publisher's webcatalogue page, where it's supposed to be free in both ADE-DRM ePub & PDF in US & Canada, which according to the University of California Press website are the only two countries they officially direct-sell their ebooks to.
Unfortunately, no working Add to Cart button, but if you neglect to mention that last bit, maybe some of our more enterprising US members would care to Report A Lower Price?
Or maybe it'll just eventually show up in other outlets and still be free then.
ETA: Oh hey, here we go: also free @ eBooks.com (ADE-DRM ePub & PDF available to Canadians, at least). Editing into the OP.