I don't think it's fine, because of two reasons. First, alloy ammo becomes obsolete long before it's available in quantity, perhaps excepting market-bought rounds from M.A.G.M.A. Although those also cost an arm and a leg, but I suppose frugal use will last you for a while. And second, alloy use is inconsistent, not only between armour/aircraft and ammo, but also between different types of ammo.
26+ rounds of big bad HMG ammo vs 6 magnum rounds for a revolver or 11 tiny pistol bullets vs 1/4 of torso+joints protection or 1/6 of a full-body riot suit. It's the same issue that was discussed
here. Realistically, a set of armour plates - never mind a full-body suit - should take
at least two-three orders of magnitude
less more alloys to make than even the biggest round you can fire from a rifle without knocking yourself out.
And even discarding realism, it doesn't strike me as conducive to good gameplay to have one-off items like armours cost peanuts compared to consumables. It's the same thing as all the horribly inflated prices in many CRPGs that make players ignore most store-bought items altogether. I don't really know why developers continue doing that time after time. Because of tradition?
Anyway, back on topic, neither do I see any benefit in making a small, dinky pistol round cost less than half the materials needed for a HMG bullet
ten times the size and something like 3-4 times the damage.
At the very least, bullet costs should be more consistent between different guns. Alloy availability is already an enormous hurdle that makes you use your stash with great deliberation.