Meduseld – I understand what you are looking for but have a feeling you won’t find just one program (especially free) but may have to utilize several to accomplish your objective.
I em’d a friend still in international finance/venture capital and asked what software they use (they own fleets of cargo vessels and other infrastructure and commodity investments that they of course expend a great deal of effort regarding modeling what if scenarios) The basic software they use is this. They have an IT department and a risk management unit however and this software costs in the thousands.
Explaining basics of what you were looking for and why, he suggests that you look here. He thinks that this is what you are looking to do? The softwre company that makes the software they use, based here in CA is ESRI. have a version for home use. Go HERE. He hopes that helps you and wishes you well. (He grew up in Rhodesia).
Hope that helps you somewhat. Bless you.