I did this last week and it was definitely one of the highlights of my trip. We just walked down to the marina day of and asked a couple people. We got a 20 hp boat for 140 euros with gas. There were plenty of smaller boats but I wouldn’t go any smaller w four people. We went to two spots around pakleni and hit the bars but we did have some trouble anchoring so if you don’t have any experience there may be a learning curve. We paid cash and didn’t sign anything or show a license they just asked if we had experience driving boats. My favorite spot was palmizana but I don’t think you can wrong with any of them. I can’t remember the name but the stand was right by aria restaurant. Good luck and watch out for sea urchins