I'm guessing most people who come to Pismo Beach is taking a road trip on the SoCal Coast. If so, depending on what kind of car you already own, I would likely suggest that you rent a car. Why? Because of a few reasons...
1) Get a car that's fuel efficient. We were driving from LA to San Jose and getting a car that has 35 miles to the gallon was super cheap on gas. (Ford Fiesta) -not bad!
2) Less wear and tear on your own car. Some of the roads up the coast are super twisty. The breaks on the rental car were going, but since it was a rental, I wasn't very concerned. It's about 600 miles roundtrip and that's a lot of miles to add to your car in a short time.
3) It's cheap. Avis was about 80 bucks for an entire weekend. If you are a group of 4 people, that's $20 each to rent a car for an entire weekend. Not bad at all!
4) The car gets DIRTY. I'm talking like caked on bugs on the bumper and such. Better to do that with a rental car than your own.
In addition to the above, I recommend you have a portable GPS or an iPad/iPhone with a GPS app. It was the single most useful tool to travel with. Music, GPS, and finding things to see, places to eat are super easy with an iPad.