I think the bigger drop off will come from massively reduced EPL payments in League One. Championship clubs without parachute payments got about £4.5m this season. Not sure of the figures for L1 and L2 but there is a steep reduction.
TV revenues are in the range of £10-100,000 per match in the Championship (I think £10,000 to away teams) but the amount depends on the day and time slot, and probably an assessment on attraction to neutrals.