The first step is to grab the required files. You'll need this Python script and the prices.txt file that it references; just a heads-up: the prices file is almost 1MB. Make sure you save both of them to the same folder, preferably one that is easy for you to access. I realize it might seem shifty at first, but I assure you there is nothing malicious in the code: some proof of such.
So, now the hard part for the not-so-computer-savvy. You're going to have to access the command line! If you're on Windows, click Start -> Run; in the dialog, type "cmd" and hit Enter. Users of other OSes will likely know how to access their terminals. Once you're in the terminal, you'll likely be in your user directory. Type "ls" to "list" the contents of your current directory. From there, you need to use the "cd" command to change the directory you're in until it's the one where you saved the files. Enjoy a simple visual demonstration:
Yes, I named my computer after Ada Lovelace. Anyway, your setup will likely be a bit different but it's fairly simple. You probably won't have to move "up" into a higher directory, but if you find that you need to, you can just use "cd .."
Well, once you "ls" and see that you're in the directory containing the files, simply issue this command:
and it will start running. It will ask you for your username and password. Don't worry, it obviously doesn't do anything harmful with the information or SL wouldn't have approved of it. Still, I didn't bother with not making it show up because of how annoying it can be to make that work correctly on all systems. Just make sure nobody's looking over your shoulder when you type it in. After that, it will go through and calculate the various pieces of data. Once it's done, it will open a file called "results.html" in your default browser and give you a nice big recap of the information it collected, to include showing you the items in your inventory, shop, and SDB sorted by value. Hopefully you'll find a gem or two tucked into the corners of your deposit box.
If there's enough interest, I'd be happy to give it an interface, but I was mostly interested in the data. Additionally, it seems the Codex team are working on an account pricer themselves which will likely be much more full-featured, so it seems counter-intuitive to go so far on what was meant to be a one-off. Either way, looking forward to your feedback.