Per-Unit Pricing
Per-unit pricing represents the basic way for billing products: All items have a price of the type Default, which becomes the unit price in the invoice line items.
The invoice line item subtotals are calculated based on their quantity multiplied by the per-unit price. For details, see Invoice Line Item Calculation.
All billing types support per-unit pricing. That is, you can use this pricing model with one-time, recurring or transactional (usage-based) items.