Are cheap fountain pens actually any good?

Yes, with caveats. Reviewers we read generally agree that sub-$30 pens like the Lamy Safari, Pilot Varsity, and Hongdian Black Forest punch well above their price. The skepticism in specialist communities tends to land on rebranded white-label pens (Wordsworth & Black, Scriveiner, Ellington, Beiluner, Fanstik) where the markup is for packaging rather than nib or build quality.