In following link listed out unit cost associated with API.
For nlapiDeleteRecord and nlapiSubmitRecord Shown unit cost as below,
When used on standard transactions: 20
When used on standard non-transactions: 10
When used on custom records: 4
Transactions: salesorders, invoices, etc.... Found under transactions menu
Non-Transactions: customers, contacts, etc...
Custom Records: Records that are not native. These record types start with "cust". They are found under customization>Record Types