My DD had it done on the ship in the crown style. With tip, I paid $35 (I think it was something like $28 for the actual braids). Yes, you can swim with them in. As far as washing goes, you gently rub shampoo around the hair, and rinse thoroughly. No conditioner or they look greasy. You can still condition the loose part at the bottom. My DD has a tender head, and did say that it pulled while they were doing the braids. You can tell them if it hurts too badly. The tighter it is, the longer it will stay in.
My hair is really long, and I do it up in bahama style braids (think Bo Derek in 10 although I definitely don't look like that!) when I go camping. It's definitely cooler, and it stays out of my face. We have a lot of ticks where we live, and it's much easier to do a nightly head check with my hair this way.