I wanted to know if it is possible to change the cost of upgraded ammo.

Define the weapon costs in zombiemode.csv and then include your mod using stringtable,mp/zombiemode.csv

look below

In _zombiemode_weapons, search for ammo_cost = 4500; Change 4500 to what you want it to be set

In _zombiemode_weapons, search for ammo_cost = 4500; Change 4500 to what you want it to be set

o
upgraded kek

then yeah follow that

If you want to change upgraded ammo globally, then sure, change the 4500. But ammo is actually tracked when you use the add_zombie_weapon function. You can define the cost for ammo there. Unfortunately, where the 4500 is, there is an if condition that overrides that for upgraded weapons. If you wanted each to be different, you could simply add an ammo cost to the ones you want, and modify the stuff around the 4500 area like this:

			if ( player has_upgrade( self.zombie_weapon_upgrade ) )
			{
				ammo_cost = get_ammo_cost( self.zombie_weapon_upgrade + "_upgraded" );
				if(ammo_cost == level.zombie_weapons[self.zombie_weapon_upgrade + "_upgraded"]/2 ) ammo_cost = 4500;
			}
			else
			{
				ammo_cost = get_ammo_cost( self.zombie_weapon_upgrade );
			}

I would change it in the add_zombie_weapon function and here, myself, but this way prob easier to understand.