Since existence is logically or conceptually prior to necessity, it would seem that "necessary existence" is an incoherent assertion. Therefore, what is the status of "necessity" as a modal claim? In particular, does it entail the subordination of existence to essence? Is a discussion of existence as actus essendi possible in the context of modality?
How is existence logically prior to necessity?
Mathematicians often identify something that must obey specific rules, if it exists, only to later find out that such a thing either does or does not exist, or, in the worst case, with something like cardinals between the first two orders of infinity, that it cannot be determined whether or not it exists.
This is then a case where we have modal existence independent of existence, and clearly we can have existence independent of modal existence (I need not have been born, it might have been prevented.) So I do not see where it is clear that either is logically prior to the other.
Let me give a more direct answer:
Although absolute 'necessary existence' is problematic, we face 'necessary potential existence' in every financial transaction, and it makes perfect sense to us: I can buy something worth n Euros if I have (n * r) Dollars somewhere (for some r we all negotiate later). So your question is broader than your example. I don't think you can frame the question reasonable about modality in general, since potentiality is also a mode.
Lacan adopts a convention of "the alchemists' loop" which orders the modes as Image -> Reality -> Symbol -> Image, and sees necessities as symbolic (variables in equations, and therefore really equivalent to linguistic constructs) and potentials as imaginary. So we cannot directly have necessary existence because the symbol of our need only creates a reality via an image -- the needed thing might have many forms, and only some of them can be real, we need to choose which become candidates, which is an act of imagination.
As pointed out in the comment above, however, this model may apply to rational psychology, but is short-circuited by things like quantum physics, mathematics, and various cultural institutions like religious faith.
You can also make the dodge of presuming layers of reality, an essence behind existence. But I think this is just circularity in disguise. That essence has its own existential problems, with parallel solutions. So you end up with either an infinite regress, or the loop.
The 'actus essendi' is reduced to one transition along this circle. A chair is a chair because it fits a definition, until then, it has not started being a chair (the physical exists for us by being symbolized). A rule means something only when we can imagine breaking it, until then it is not yet a rule (the symbol exists for us in an imaginary example). We take actions with effects in pursuit of an idea (our chosen images become real by production.)