Interesting
I've also wondered what more the non-free versions of public domains offer. I'd be willing to pay a couple of dollars for the effort to digitize,
check and publish a public domain book, but not if all they're doing is taking something offered by a community of volunteers and just slap a price tag on it.
I haven't researched ebookprice.info very thoroughly, but I did make a search on an author's name and it seemed to work. Probably more reliable than a title search.