They do charge you extra, but it's a pretty small charge. I found it great to have someone there with me. It's easier to take short walks with someone there, and getting help doing stuff you simply weren't feeling up to doing, like going across the street for food because the meals they served were so bad :-)
Remember, you will have to deal with airports as well. I had to take Heparin(sp?) shots on each leg of my flight and I really didn't want to have to do that myself.