It really depends on how likely you are going to be caught and what the consequences are. Your ISP may not care but copyright holders generally band together and have legal set ups in most countries both trying to take down servers and end users, lobby for legal changes including trying to criminalise copy right infingement.

Generally a trustworthy VPN is a very good idea not just for torrenting but for maintaining privacy and security when you are doing other things such as banking, or even just browsing. A VPN is about protecting all your data and internet traffic, not just protecting you when torrenting.

In terms of Torrenting, a Proxy may be enough and a lot of the best VPN providers do provide Proxy servers (that anonymise the detail of your Torrenting use but the rest of your computer use would be on the open internet) in addition to full VPN connections that secure your whole PC for P2P and non-P2P uses.

If a VPN seems too expensive, then there are companies that also only provide Proxy connecftions. BTGuard.com is an example; the Proxy only option is 30% cheaper than the full VPN option.

EDIT: Note though, a VPN is about anonymity. You need to trust your VPN provider as you're passing your data through them, and it is not a substitue for secure practices on the internet. You still need to be secure on the internet including only downloadling from trustworthy locations, using antivirus and malware protection, not installing software from insecure places, using HTTPS and securing your internet browser, turning on tracking protection & ad blocking, and even considering using virtualisation to protect yourself even more.