Realistically you cannot compensate for recurring charges with one-time charges. The former you know, the latter you do not have any idea whether they will occur or not. Thus, while xfers could be invoiced at cost plus principles (or whatever), budgetarily it is insanity to assume that such events would occur.

I like the gym analogy. Although most have different categories for different kinds of members, whether you can go to group lessons or not, whether you train during busy hours our outside of them, etc. as well as the implicit assumption that most pay but do not use. Also, they sell t-shirts, towels, chocolate, energy drinks, porridge, etc.