The ItemPricing sublist is located the Financial subtab in Customer record. It contains the columns Item,Price level, Currency and Unit price by default. It is not possible to add a new column to this sublist through the standard NetSuite form/field customizations. Here is a sample code to add a custom column in UI which can act as a virtula field.
const beforeLoad = (scriptContext) => {
var form=scriptContext.form;
var sublist = form.getSublist({
id : 'itempricing'
});
sublist.addField({
id: 'custpage_testfield',
type: serverWidget.FieldType.TEXT,
label: 'Test'
});
}