I'm working on Hebrew fonts (practically, finished).
I would like them to contain a full roman-character-set glyphs.
Is there any royalty-free Roman font I can use for that?
You might want to check around and see if GhostScript or FreeType comes with any freely distributable and modifiable fonts.
Note that this has to do with more than just not paying royalties; the font software license may place other restrictions on what you can and can not do with the font.