Explain Budgeting processes and techniques

The Custom racing aircraft are the product of the Acme Flying Machine Company. It designs as well as produces these for professional race teams. They develop as well as build these custom designs as single individualized units or for the ultra-rich in many up to 4 units. The orders are generated by the marketing as well as sales department, with assistance from the owners who participate in the management of the company. Each new order is allocated to a project team, which starts by making an approximation to the customer before a contract is signed. The project teams have a great contract of experience in these projects.

As would be predictable the owners are hands-on and have opinions on the estimates. The marketing folks moreover provide suggestions on what the customer is willing to pay.

What are some processes as well as techniques that you would suggest to make the budgeting process work well? Start with more general however also provide some specifics as related to creating detailed project budgets. Be sure to validate why you think your recommendations will work.