Steve Gardham wrote:

Personally I'd rather have access to Percy's other manuscripts of all the ballads people sent him and the correspondence.

I have sympathy for that viewpoint, but that's a much harder task than just scanning the Percy Folio; it would take someone tracking them all down and figuring out what is what. Harvard University has some of his papers, but it's not clear that it is all of them or exactly what is in there.

https://hollisarchives.lib.harvard.edu/repositories/24/resources/1606

I believe there is a fairly recent book on this but if I remember aright it was beyond my pocket.

If you're thinking of Nick Groom's The Making of Percy's Reliques (and I'm not sure you are)... you're right, they're charging absurd amounts for it now. But it's not worth it. I have it, and it's mostly about the process of putting the Reliques through the press, not about the gathering of the materials themselves. I'd also say it's too kind to Percy. Not really much use to ballad scholars.