If the conveyor is like most, drying agent is probably only needed for the basic service.
For example, if tri-foam (containing natural or synthetic wax), clearcoat, rain-x or hot wax is applied during the wash, drying agent is not needed.
In fact, it’s not recommended. Some of my clients barely use any.
Best bang for buck is drying agent that contains mineral seal oil. It is active ingredient in hydrophobic (water beading) drying aids.
Since mineral oil is mineral oil, buy the cheapest.
Most claims of drying aid superiority are just claims.