What factors determine application fees?
Application fees are primarily there to moderate the number of applications and in the case of universities receiving huge numbers of applications partially finance the application process. There is of course many services for which one can argue to cover costs. This includes personnel to handle applications, personnel to evaluate applications, costs for paper handling (at least earlier including postage if anything had to be handled through regular mail). When looking at the costs for taking in the money and possibly distributing it within a system that likely involve many persons it becomes clear that a well defined cost analysis is not likely done, it is not cost effective. Instead the pricing can be used to signal, for example, prestige and to ward off chance applications. The level of the  pricing will likely be determined by these factors but also include considerations to what levels will be reasonable for the uptake of students visavi ethical and social goals for the university. In short, the pricing is more of a tool "for" recruitment than a precise estimate for the costs involved in the application process.