Coursework re-moderation, as its called, is not as straightforward as remarking an exam.The guidance says:
Candidate consent is not required for post-results review of moderation as candidates’ marks may be lowered but their published subject grades will not be lowered in the series concerned. However, centres should be aware that a lowered mark may be carried forward to future certification. For example, if a coursework mark which contributes to an AS award is lowered as a result of review of moderation, the AS grade will be protected, but the lower mark will contribute to any subsequent A-level award.
Review of moderation cannot be undertaken upon the work of an individual candidate or the work of candidates not in the original sample.
So your school would have to pay for ALL the coursework to be re-moderated. If your centre had more than 20 students then they won't have sent off all the work, only a sample. The remoderation will be on the same sample.
Also it costs £213.75 to re-moderate a unit