Dave Hulett has a whitepaper on his web site that covers an introduction to cost risk analysis. If this is a new subject for you, this whitepaper goes through a number of quantitative considerations, including correlation risks among cost elements, that will give you a good feel for this territory.
You might also take a look at a more thorough treatment by reading through the cost estimating guide from the General Accounting Office (GAO), an arm of Congress. One thing about this guide is that is well illustrated with a lot of diagrams that point the way.
Of course, NASA has a readable manual on parametric cost estimating. Take a look at it if you really want to dig deeper into the subject.
