|Steam Gauge is working, please be patient...|
You may have noticed that Steam Gauge only returns the Steam store price of a game, and not the amount you actually paid for it. This is because Valve does not allow access to your Steam transaction history by outside parties (this is a good thing). However, you can still see a transaction history of your account on Steam's website at: store.steampowered.com/account
Click and drag this link to your bookmarks:
Steam Receipt 2.2
Steam Receipt 2.0 was designed to be locale agnostic, but is difficult to test in every situation. If you notice an issue, feel free to drop me a line. If you'd like to make your own, feel free to fork off this GitHub repo.
Steam does track key redemptions (from game bundles, retail purchase, etc), but has no way of knowing how much you paid for it, so those costs are excluded.
Because of in-game transactions and Steam wallet funding (which are not known to Steam Gauge), it is possible to have spent more on your Steam account than it is "worth". That said, it could also be a bug (the script doesn't support non-US currencies at the moment); feel free to shoot an e-mail over to firstname.lastname@example.org with details, and I'll try to get it sussed out.
Yes, but you should never execute code on web pages with sensitive information without understanding what it does. To facilitate this, I've posted the bookmarklet code in easy-to-read form on GitHub (also, you can view the source directly in the bookmark link).