Agreed. Although the iPad Pro is large enough to display a whole sheet of paper at native scale, I find that the smaller 6th generation iPad works just fine too at less than $400 (it also supports the first gen Apple Pencil).

Apple Books (previously iBooks) works well enough for annotating and searching PDFs and ePubs, although Notability is much faster and works more like paper.

Agreed on a refurb iPad Pro or even Surface depending on your needs.