I want to make a mod that cuts out the need for going to merchants.

I was thinking of making a chest that you add items into and cast a spell on it to turn everything inside into it's gold value, but I need to know how to check the value of an item that is in the chest. Anyone know how?

Well it's impossible to get an item reference for an inventory item just like that right now so you might want to use getactivemenuselection on the item in the chest, which makes a reference out of the object you are currently hovering your cursor over, which ofcourse rules out a spell. So you can make a condition that if you press a key(or even a key combo) of your choice and hover the cursor over the item, it calculates the items value and replaces it with gold.

Erhm, isn't it as simple as calling GetItems on that container, then iterating over the elements of the array and calling GetFullGoldValue on every item? You only need the base object for that.

Sure, if you're not afraid of array scripts

True. You will get rich extremely fast with such a mod though - unless you tweak it to only give a percentage of each item's value, but then again, that may be what you want.