Three $(3)$ method of cost estimation:

$1.$ Engineering method: This is a detailed approach where you estimate the cost of each part of a system separately. It's usually done when the design is final and there's a lot of technical data available. While accurate, it's time$-$consuming and costly$.$

$2.$ Account analysis method: This method looks at all cost accounts and separates fixed and variable costs. It creates a simple model to show how total costs change with activity. It's easy to use but relies on judgment and might miss complex cost details.

$3.$ Regression analysis method: This is a statistical method that finds the relationship between factors that affect costs. It$$s useful for making cost predictions, but it needs a lot of good data and a solid understanding of statistics.