The costs can include but are not limited to sound engineering, equipment rental, studio rental, session musicians, and mixing engineering. Generally, a studio will be booked for a predetermined number of days and an estimate of the total cost will be presented to the renter. That said, unexpected costs can accrue depending on the size of the project and the services required by the performer. Regardless, when the work has been completed, the party responsible will bill the musician(s) using an invoice that describes both the total cost and the date by which the amount must be paid.