Working as an IT Architect often requries fast evaluation of the projects costs to make a rapid judgement on whether the costs exceed the benefit. Most of the time I use a spreadsheet to quickly lay out costs and decide whether it passes the sniff test for ROI.
More recently I started using Soulver. Here is a demo and why you might be interested.
Some more info on Soulver follows:
Soulver Home Page – cost is $12 on the Mac App Store
Soulver Product Demo on Youtube.