Good question, since you've always used a car in the past than I would suggest getting a car if it makes you more comfortable. For that price, the convenience of picking up supplies at a store might make it worth while. As far as buses go, this will be out first trip to the POP also, so I can't give you a first hand account. From what I have read here, it is pretty good overall. That said, people have also had issues with it from time to time, but I think that's the case with transportation in general. There is nothing preventing you from takeing the bus sometimes and your car others.
For the price you can get a car for, I wouldn't mind trying to talk my brother into renting a car for the week. Of course it would cost us more, since we are a party of 5, but it would make some aspects of our trip better. Not gonna happen anyways, he like to use our as a mini vacation from driving anyways. As the fifth wheel in our group, I'm fine letting him do whatever makes him more comfortable.