Hi Warren,
one of the main inputs to determine budget process is the "Activity Cost Estimates", if you refer back to section 7.2.3.1 in the PMBOK guide, you will find that activity cost estimates" includes, but is not limited to, direct labor, materials, equipment, services, facilities, information technology, and special categories such as cost of financing (including interest charges), an inflation allowance, exchange rates, or a cost contingency reserve. Indirect costs, if they are included in the project estimate, can be included at the activity level or at higher levels."
hope this helps.