Seedboxes are great if your going to do a lot of torrents up and down, or as in your case a monthly data cap. You can transfer the files from your seedbox via encrypted FTP, and your ISP only knows that hey your transferring a lot of data (don't know what it is, just that its a lot). If your a casual user, seedboxes may be a bit expensive.
Here's an example, my VPN is actually a Virtual Server running my DNS and VPN only. The only thing I torrent is the occasional OS upgrades. My service allows 1TB of data transfers. I transfer directly to my server via encrypted tunnel (setting upload to 0 - yea I'm that guy). $4 a month, and I can use my vpn on my phone to protect my data and never get near my 1TB limit.
Seedboxes you have to store the data on the Seedbox, so even though most give you unlimited bandwidth on transfers you have to pay for storage. For $5 a month, Seedboxbay will give you unlimited bandwidth at 1Gbps but only 150GB of storage. That's ok, but if we're talking terabytes, say over 2TB, Seedbox.IO is about $28 a month. For a hardcore torrenter, or a person with a cap (or both) that's fine, casual user not so fine.