but your saying that a ship maint cost that today is low could skyrocket if some AI I dont even know about orders a bunch of ships with that weapon using that material?
It's possible, though not particularly likely. Budgeting for it just means leaving yourself a bit of extra cashflow, or if you really wanted to do so you could compute the worst-case maintenance cost since resource costs are capped and budget the fleet that way. Aside from that, it's pretty easy to ignore as once the galaxy is fairly well developed the resources will typically cost somewhere around 0.8-1 credit per unit. It's also unlikely for a resource's cost to remain high for an extended amount of time, as the computer-controlled factions and any automated constructors will eventually get around to adding mines for high-cost resources, and if you're paying attention to resource costs and what your own constructors are doing you can help prioritize these.
The big resources to watch out for, as far as costs go, are polymer, carbon fiber, and chromium, as these three are somewhat rare and are used in a number of common components (especially engines and energy collectors), and also steel. Steel is a really big one if you're going with heavily armored designs, as low-tech armor in particular can use enormous amounts of it when you stack up twenty or thirty plates on a single ship, and steel is also used by a fair number of other common components, though it's also fairly easy to find a number of decent sources for it. You should also keep an eye on hydrogen, especially if you're getting to the point in the game where you might start switching over to it as a fuel gas.