INTERNET SACRED TEXT ARCHIVE
There's a lot of really useful stuff for folklorists, and people like me who make our livings stealing from them, at The Internet Sacred Text Archive.
I was just looking for Robert Kirk's 1691 book The Secret Commonwealth of Elves, Fauns and Fairies
and could only find it at Amazon for $125. Which is a bit stiff for a late reprint. It's free on the ISTA. For $50 they will also sell you a CD-ROM containing all their stuff.