The most frequent crossings to Spetses are provided by Hellenic Seaways with their hydrofoils called Flying Dolphins or the larger (and more comfortable) Flying Cats. These Flying Cats are now a brand new lime green colour, as of 2013! Hellenic have sailings daily throughout the year and only get cancelled in severe weather during the winter, which isn't too often.
Flying Cats & Dolphins
Flying Dolphin and Flying Cat hydrofoils
Price range: Return trip from Piraeus to Spetses on Flying Cat: €70 (2013)
If you travel down by car taxi or hired car then you will arrive at the Port of Kosta. You have a choice of travel to Spetses Island (depending on the time of the year and time of the day)
You can take a caique (kaiki) in the summer months (May - September) and they will go backwards and forward all day and early evening. You will have to wait until it fills up though and the journey time is approximately 20 minutes. Cost is approximately €4. There is a child price for under 5's (Usually half price).