Depending on what you are looking at estimating - is it dealing with metals, plastics, chemicals, etc.?
For manufacturing type estimates, both internal and external, Costimator works quite well by developing a process routing to various equiment/workcells(www.mtisystems.com) but does require a...
J. Wiley Publications www.wiley.com/WileyCDA/ has a large number of reference manuals in regards to cost estimation, look up the website, and do a product search for "estimating" and you should find 10 or so titles available. I've used the "Cost Estimator's Reference Manual, 2nd...