New Bank Plugin!
Built a plugin called Bank Watcher (look for the treasure chest with an eye icon) that tracks changes in your bank's value over time.
The "Top Movers" filter, shown in the screenshot, sorts your bank by biggest price swings so you can quickly see what's gained or lost the most value since you last checked.
It just got merged into the official Plugin Hub, so you can grab it straight from the plugin list in client, no sideloading needed.
Happy to answer questions or take feature requests!
-EDIT
https://runelite.net/plugin-hub/show/bank-watcher
Also, please check out the plugin hub page for the Bank Watcher plugin to better understand how to use it. I just wanted to clarify that on your first scan that you do for the account, there will be no data such as Top Gainers and whatnot. After that first scan, it's probably best to wait maybe 2 to 5 hours before scanning again, since prices likely won't move significantly unless your total bank value is in the billions. I can't really test this myself since my bank is only sitting at 80M, so if anyone here has a bigger bank, I'd love to hear if that holds up!