I pondered this myself and never got around to it. You don't want to pay with anything that can be tracked back to you or it defeats the entire purpose. What I would do is find one that accepts gift cards, or those prepaid credit cards. Buy the cards with cash around Mothers/Father's day, Christmas, etc (you will just blend in with everyone else doing it) and then wait a bit to use them, then use them. The idea is if someone does try to track a particular VPN account back to a particular person it will add an extra layer of difficulty. They'll see a gift card was used to pay for it, then they'll request CCTV footage of the store it was bought at, but then they won't know which person actually bought it because there will be a lot of them. One flaw with this logic though is there will still be the fact that your real IP is connecting to the VPN server. So you still have to trust that they don't log stuff. The money transaction part is going to be tracked in the financial system, so that's why it's still good to cover up that part.
I want to setup a vlan where anything on that vlan exits through a persistent VPN but have not done enough research yet to see if there are any services that support this. I imagine anyone that uses a standard VPN system like OpenVPN it should be doable. I basically have a VPN client act as a default gateway and then connect to the VPN. Then set firewall rules to block all traffic going out except for the VPN server. Going to experiment with that some day but one of those things I don't necessarily need bad enough. Probably a good idea for torrenting though.