There are signs all over Bodrum for 'KOS 12Euros.' This year we got a chance to see what all of the fuss was all about. I bought the tickets from a local travel agent in Turgutreis that had a sign advertising this on its window. The cost of a round-trip ticket is 12 Euro's if you return the same day and 15 Euro's if you return a different day. The ferry leaves from Turgutreis at 9.30am they ask the travelers to arrive at the port (which is the last door of the Turgutreis Marina) around 8.45am. It is wise to arrive early since if you don't want to end up waiting under the scorching sun for half an hour. Unfortunately the ferry is not air-conditioned and can get quite uncomfortable so my suggestion is to bring a hat with a wide brim and sit upstairs in the open deck. It is only about a 40minute ride to Kos from Bodrum. Once the boat docks, try to be one of the first ones of the boat since passport control is extremely slow and can take up to an hour to an hour and a half.
Having said all of that, Kos is a lovely little island with quite a bit of diversions. It has a bit of history making it worth while to walk around and learn about the different civilizations that have past through this geography plus a lot of photo opportunities.
I didn't get a chance to go in the water but I have heard people say nice things about it. Bodrum has such nice beaches that walking around the old part of town and driving to Kefalos which is the other side of the island seemed more appealing to us.
This is the cafe right behind the castle. I saw a sign for cold lemonade and stopped for a drink before proceeding to the port for the ferry to go back.
On the way back, I sat out on the top deck of the ferry and got a nice, even tan. I plan to go back again next summer, maybe for a nice meal at a taverna by the sea.