if you are going to subscribe to vpn to bypass quota, why not subscribe to mega instead? Even the lowest plan is fine (1tb transfer) if you are not a heavy downloader. I think it's cheaper if you use google play.
My approach may be not most anonymous, but it gets the job done. I'm downloading from multiple free VPNs. That's it. If I exhaust quota, just switch to another one.
This is what I do also. Can be a hassle switching and finding an IP with free quota but it has worked for me so far. I do not DL a lot though nor do I automate the process.
I'm on Linux with PIA. I made a list of geographically local regions and my script picks one at random then runs piactl set region $randomregion
On the JD2 settings page, go to Reconnect. Check all 3 boxes. Set reconnect method to External Tool Reconnect. Put the absolute path to your script. If you have PIA I can try and post my little script, formatting on mobile isn't working.
Protonvpn has a browser app where you can turn it on so it works on your browser traffic but not the rest of the network ( e.g. steam ). I haven't tried it much so I can't say how well it works or how stable it is.
The problem with downloading over http is that if it fails you'll usually need to start over completely. And that sucks if you're pulling in big files like.... Linux ISO images.
If you're downloading a lot over http I'd suggest finding a download manager. Those usually have some kind of resume download functionality.
Perhaps there is one that allows binding to the VPN interface?