I've seen on my work place (a University) most students making the software estimation cost of their final diploma work using COCOMO. My guessing is that this way of estimating costs is somewhat old (COCOMO dates of 1981), hence my question:

How do you estimate costs in your software?

I've seen things like :

Cost = ( HoursOfWork + EstimatedIddle ) * HourlyRate

That's not what I want, I'm looking for a properly (scientifically) defined cost model

EDIT I've found some related questions on SO:

• What are some of the software cost estimation methods and models?
• How do you estimate the cost of developing software requirements?