i will agree on the low prices of santorini in Oct. i would not rec though the spead ones. basically according to the Greek shipping law no boat/shit can get out of a port when the winds are 8 or more in the scale of Bofor (not sure of spelling). for examble for friday 22/09 is expected to be 7. that means if by any chance in Oct wind is strong no boat will travel.
On the other hand the spead ones are more vanurable to the wind and their limit is lower. I dont know up to what bofor they have the ok to travel but i believe 6-7 is their limit.
also the spead ones are expected to stop at some point in oct.