XKCD Comics Permission
You’re more than welcome to do this at no fee.
If you would like high-resolution versions of the comics, it may be difficult — we don’t have them all in an easy-to-distribute format, so you’d have to ask for them from me on a case-by-case basis. But if you’re printing small enough that the web-resolution versions work, then no further permission from me is needed! Just attribute them to xkcd.com somewhere near where you print them.
Best,
Randall
Randall Munroe <randall@xkcd.com>