Early project estimates are just that, your best estimation of what it is going to take to deliver the project. There are a few techniques to help you create a reasonable estimate. You could try expert judgment
, which uses subject matter experts to calculate the total cost of the project. You could use analogous estimating
, which looks at the history of similar projects and how much they cost while taking into account any differences in the new project. There is also supplier bid analysis
, which compares bids from different suppliers to arrive at a cost estimate for the project.
This article may help with some more information about creating budgets, Creating a Project Budget: What You Need to Know
. It contains a Business Analysis and Forecasting Template you may find useful.