I do the same. Using VPN, proxy, Firefox container, tracker blocking, the whole 9 yards. I haven’t seen price change based on location/purchase history. I’ve been looking for signs of this for a while. Prices do fluctuate quite a bit though. The site might have auto-selected a different “ships from” option for you, depending on how you’re logged in.
I use Calibre and its web server locally. Works great.