I have a similar length trip to the OP and am seeing the same prices. An alternative is the Business T5 car park is about £55 and only adds about 5 mins to the total journey time (and drops off at the Southern end of departures which is better for premium check-in desks) versus Pods.
However, those are pretty much the standard drive-up prices for Business/Pod parking (28 and 34/day respectively) so no need to book in advance, unless an offer shows up in the days before your trip.