Assaults always carry a range of grenades - they’re not too expensive and very useful, especially the incendiary ones. Snipers or berserkers might carry a spare acid pistol for the big boys, or a paralysis pistol if i need to capture something, again not too expensive. The high end guns are indeed pricey but I never have that much trouble, except for some of the shoulder mounted weapons, which are punishingly expensive.
Honestly I find armor my major cost the whole way through - you can’t find it lying around and it doesn’t drop if your soldier dies, which is incredibly annoying. A full suit for a heavy costs damn near as much as a plane, which seems pretty silly.