A unit cost is provided in the quotation based on development requirements, product specifications, and forecast quantity. The quote combines development charges and unit cost.
Your volume forecast must be confirmed before the signature of the contract as the unit cost is based on this forecast. Future deposits are computed based on the total order value.
At this point agreeing on a milestone and payment schedule with the partner you choosed is a must. It will help both parties to prepare the financial resources with a clear milestones in mind.