I didn't read all of your linked article but this might help: http://www.farmdoc.illinois.edu/pubs/FASTtool.asp?section=FAST

It is a list of excel spreadsheets developed by U of Ill that may simplify what you are trying to do. If you scroll down the page there are a few different ones on Investment analysis, mach mgmt and so on. They are not large files for the most part. Hope this helps.