There are some "free" Vpn providers but I'm pretty sure that speeds will be crappy and they might block you based on traffic level (since you want torrenting), even if legal stuff which I assume is want you want to torrent *coff*coff*
There is no Torrent program that hides your IP address, but there are some programs like PeerBlock which blocks known IP addresses that are being used for surveillance but leave the unknown ones, means you are not totally safe with it. Only Betternet allows Torrenting on their servers but I wouldn't recommend you that because firstly, they share your information with third party advertisers (e.g. cookies) which is written in their privacy policy.
If you are Torrenting files that are open to public like Ubuntu ISO then you don't need any VPN. However, if you occasionally download *cough* things then you need to subscribe for a Torrent VPN to hide your IP address in order to stay anonymous (via VPN) while Torrenting.
An old version of Transmission (V2.11) allowed you to setup a proxy address - I used that for a couple years before I finally signed up for PIA VPN service 2 years ago - because using a proxy is not as safe (and why Transmission says they removed the ability from versions newer than 2.11).