How to display Monthly Project Costs in an Excel Calendar Overview? ConditionalFormatting?

Dear all,

I've searched this but haven't found an answer yet.
I'm working on a costing spreadsheet that calculates the total effort for each of a variety of projects. Now, what I'd like to do is to simulate the monthly cash drain by applying various scenarios of sequencing the starts of the projects. Ultimately, I'd like to have a cash drain chart, showing how much money I will spend per month depending on the project implementation sequence.
I added a tab that displays the next 60 months in the X-axis (row 1) and the project names in the Y-axis (column A). So, whenever I type an "X" marking the project start under a certain month, I want Excel to indicate the end of the project (using conditional fomatting) and divide the total cost of the project by the amount of months between start and end. Each cell between start and end should display the monthly cash drain for the project, so that at the bottom of the overview I can summarize the monthly costs over all projects.

It sounds extremely complex to me but probably has a simple solution using a nice formula and conditional formatting...

Thanks in advance for your help.

Inwardglee