Buy one now AND then, that’s my plan.

Using macros you COULD do it in the same cell, using standard formulas your have your input in one cell and your output in another. Classically the second route is preferred so that you can see the exact cost and impact of each line item, including tax.

I’ve been using a .txt for professional notes for decades. Make the first line .LOG and, on Windows at least, notepad will add a time stamp to the bottom and start you below it.