The two main methods of estimating costs are?

The bottom-up budgeting approach involves estimating the costs of individual tasks or work packages and then aggregating them to arrive at a total project cost. This method is detailed and thorough, as it considers all aspects of the project at a granular level.

On the other hand, top-down budgeting starts with a total project budget and then allocates amounts to various parts of the project based on estimates or historical data. This method is less detailed and often used when there is a lack of detailed information about every aspect of the project.

Both methods have their advantages and are used at different stages of project planning or when different levels of information are available.

References:

Project Cost Estimation: How to Estimate Project Cost1.

Estimating Cost of a Project: Techniques and Examples2.

Project Cost Estimation Tools and Techniques - PM Certification3.