In 1823 the British government was discussing a modest increase in the size of the army, which had been drastically reduced in the years since 1815 to the point that there were no disposable troops ready to be sent to deal with even relatively minor, localized trouble in the empire. In the course of these discussions Lord Bathurst, the Secretary of State for War and the Colonies (and prime mover of the measure) told Wellington that the Horse Guards calculated the cost of an additional battalion of regular infantry amounting to 576 men to be £23,500 (presumably per annum), while a battalion of 1,000 veterans (who had been embodied as a temporary expedient) had a nett cost (deducting pensions etc that would otherwise have to be paid) of only £20,000. However Bathurst did qualify this by saying that he doubted that the Horse Guards had allowed for the saving of half-pay for those officers who were entitled to it in the regular battalion. (Bathurst to Wellington, 14 November 1823, WND vol 2 p 180)

Given that there had actually been significant deflation since the war, I think that it would be fairly safe to use these figures as a rough rule of thumb guide to the cost of British army units during the war.

Rory