I actually played around with this a little and here are the results I found:
1. While Powerpoint does give you the ability to create a table, it doesn't give you the ability to enter formulas.
2. Word does give you the ability to create tables with formulas, but you must actually embed the Word document (with the created table) in the Powerpoint slide in order to be able to update the table. To update you essentially need to edit the Word table just as you would an excel spreadsheet. Also you must enter additional key-strokes (F9) to recalculate the formula.
If i understand you correctly, your problem with Excel is the way it opens in Powerpoint, causing a change in the screen and possibly hiding other data.
A way around this is to create a simple 2 cell spreadsheet. Cell A1 would be where you enter the number of widgets. Cell B1 would be your formula (formatted to show currency). Go to the Tools menu | Options | View tab. In the Windows options section, uncheck Row & column headers, Horizontal and Vertical scrollbars, and Sheet tabs, and click OK. Highlight the 2 cells containing the 2 required cells and copy and paste to your Powerpoint slide. With the above changes, when editing the excel "spreadsheet", while the screen will momentarily flicker, the only other changes will be that the 2 cells are now outlined. After changing the number of "widgets wanted", you merely have to tab to the "total cost" cell to recalculate. You won't see the column headers, scrollbars, sheet tabs, etc. that you normally see when editing an embedded spreadsheet.
Hope this gives you the solution you were looking for.
