I don’t know if you’ve seen this, but it was new to me, so allow me to share:
Apparently there’s a pretty easy way to see your lifetime total spending at Amazon. Just go to the “Your Account” section and click on “Download Order Reports,” then take the resulting .csv file into Excel or something similar and total it up.
Full step-by-step instructions can be found here.
My total was, uh, sobering. Ahem.