Nice article on Peer to Peer versus Rental companies, some conclusions:
"After crunching all those numbers, we’ve deduced what we probably should have been able to guess: gas isn’t that expensive. On short trips, the difference between Zipcar and P2P services is slight. But on longer trips, the fact that Zipcar covers gas costs doesn’t come close to matching the cheaper rates available on sites like Getaround.
Peer to Peer sites can require meeting the car owner to grab the key, or waiting for the owner to confirm your rental request. If you’re willing to pay a premium to avoid the hassle, Zipcar is the way to go. But if you’re willing to hustle to save some cash, P2P wins hands down.”