Yes, you will pay a pretty penny for a 30' 50A cord, and at the place I am at the most with friends (private property) it takes me 3 exensions to get to my RV. Yes its a long distance, yes I monitor my power, and no I have yet to see a voltage issue even when we are all running our AC untils in the middle of summer.
So to add only one extension, you will have no issues and I have had at times to use one of my extensions at some of the other areas I have camped due to the layout of the power pedestals at some racetracks.