Hi Karen,
The minibus at Arkokal seats 12 passengers (but less if lots of large luggage). I don't have the price yet for 2012 but if I remember correctly last year it was in the region of 85 euros each way.
Contact Arkokal here for their latest price....
arkokal@otenet.gr or arkokal@arkokal.gr
0030 26630 51436/51433