'at no further charge' => 'at no charge' (section 9).

See: GPLv3 Third Discussion Draft Rationale
http://gplv3.fsf.org/gpl3-dd3-rationale.pdf p. 48, n. 52 (clarifying
the phrase "at no extra charge" which was added in GPLv3 Discussion
Draft 2).

I believe it is clear enough without the word 'further'.