It's certainly not frictionless, but not too much work, either.

I keep a sheet where I manually enter the tracked purchases as I make them, like this:

(A lookup table of the items I'm tracking autofills unit names given an item's name)

Another pivot table then helps aggregate monthly average sats/unit prices and change values per item.

Takes a few minutes for each purchase because we usually buy more than just the tracked item(s) with sats. So I break out the fraction for each tracked item from the total price.
But since I pay the full bill in sats, that's an easy calculation.