If a typical year schedule at the $80,000 per year college is two semesters with four classes each, then each class costs $10,000. Obviously, the best ROI in academic terms would come from (usually upper level) courses whose content is not readily available at lower cost (e.g. community college or high school AP).
Of course, lower level foreign language courses are not the only “not the best ROI” uses of schedule space in college. The common practice of repeating one’s AP credit in math or other subjects that the college is willing to give advanced placement for is another.