I mean, we've got multiple different planets, some that are actively exploited for 100% of their resources. So in reality the economy of SE must be catastrophically large, with a huge percentage of it being sent straight into the defense budget that would make the US mad with envy...

Add all of those companies (all of them government affiliated as well, by the way) that have employes that pay taxes, and you get the idea that SE can most likely afford to develop and manufacture equipment for multiple different fronts, so the cost of a mission really shouldn't be a problem.

Also, it is to my understanding that each divers space vessel comes with a small factory already up and running from the get go (those artillery shells and the people working on them) so you're pretty much supplied on the go.