Here are the bus schedules between Castelvetrano and Selinunte:
http://www.autoservizisalemi.i..._urbane.php?linea=11
From Castelvetrano, you can get to Mazara del Vallo, Marsala and Trapani by train:
Castelvetrano to Palermo by Salemi bus:
http://www.autoservizisalemi.i...=12&data=20-10-2009;
Castelvetrano to Agrigento by Lumia bus:
http://www.autolineelumia.it/o..._a=AGRIGENTO#ricerca
You must always make a connection in Castelvetrano to get to and from Selinunte.
Here is a previous posting: