Have a look at the image below and the attached workbook. You don't describe where the up-front cost is stored. I assume it's in your data, but I used a parameter and one Sub-category. I used a Running Total calc to work it out. Hope this helps.
Andy, that's great! And that's exactly what I'm looking for....the next step that I'll work on is including multiple categories, each with their own cost, into the same view.