[VXA request] Items as currency

Um, hi everyone. This is kind of complicated, so please bear with me! 
I'm looking for a script for VX Ace that lets me use items instead of gold as currency- basically, a barter system.

My game is set in a post-apocalyptic world, and people there use ammo instead of money. So conserving ammo in battle is very important- you'll need it to buy things! And since there's lots of different calibres of bullets, I'd like all the different calibres (9mm, 5.56mm, 12.7mm and so on) to be organised under a generic "Ammo" stat that you see in the main menu where it'd normally say "Gold". But, go into the items/equipment menus, and you'd see all the different calibres that each character uses for their respective weapons.

The other thing I'd need is for each merchant to have a type of ammo that they prefer to use (I guess by putting it into the store's inventory), and when you sell items to them, they give you that kind of ammo.

That way, you can conserve ammo by going into melee combat instead, or you can sell to specific merchants in order to gain a type of ammo that nobody in the party uses for their guns.

So... I told you it was complicated!

But would it be possible for someone to write this up?