Maybe sheet swapping would let you keep this on one dashboard. Parameter would select inventory or cost. Whichever is selected, the other sheet goes away.
If you're not familiar with swapping, here is a link to a video:
What I didn't follow in your description was what the waterfall looks like. If things are getting too cluttered on the dashboard, let the drill-downs happen on a separate dashboard. Just give the user an easy way to go back to the original dashboard when they are done. (Some users are OK with clicking tabs. I tend to direct them away from that, though. For instance if you drill from Dashboard-A to Dashboard-B and expect B to be just for the selected org, it's imperative that they get there by the user actions rather than by clicking the tab. Otherwise Dashboard-B will display with unfiltered data for all orgs. So to maintain the discipline, I give them an action on Dashboard-B to return to A.)
Thanks for your response my own research and your response have validated that "switching" out pages using a parameter control is going to be the best solution for my situation. I appreciate the informative video on how to do this.
Thanks again for your input,