William Blake's "The Pilgrim's Progress" Series

I am in the middle of reading John Bunyan's The Pilgrim's Progress. I know the plot of this book quite well, having read the children's version Dangerous Journey and watched its accompanying film a bigillion times. But, being a historian and purist, I wanted to read the original book (first published in 1687).

Although I know the story well, I didn't know that William Blake created illustrations of this famous allegory. It doesn't surprise me that Blake would be interested in The Pilgrim's Progress; as a nonconformist artist that was interested in mythical and prophetic subject matter, this story is right up his alley.

Blake began this The Pilgrim's Progress series in 1824, but it was never finished (I assume because Blake died in 1827). The completed illustrations weren't put into a book until 1941 by the Limited Editions Club, over 100 years after Blake died.

I haven't been able to find a lot of information or discussion about this series in art history databases. I also haven't been able to find a lot of images of the series. Perhaps this series has been ignored because it is incomplete?

I'm curious to see what the other illustrations look like. I might have to buy this 1942 edition (Heritage Press) off of eBay, which includes twelve of the watercolor illustrations by Blake. But I'm a little skeptical as to why this book is only for sale for $29. Doesn't that seem a little low for an old book with watercolors by William Blake?