Getting to Olympia by  public transport is common for backpackers as it is very cheap but  we do recommend you avoid this means of transport if you have children, lots of luggage, or lose your temper easily. Usually your ticket will get you all the way to Pyrgos. You then  need to get off the bus and purchase a ticket for the  remainder of the trip (20km) which also means you will have to wait for approximately 20 minutes to an hour.
 To travel  by bus then you need to get to Kifissou street 100 (else called “Stathmos Kifissou”) were the bus terminals are. There you can catch a ride to anywhere in mainland Greece. You need to ask for a ticket to Pyrgos.  The bus travels the route via Patras. 
The phone number of the Kifissos station is 210-5134110 / 210-5124910.

More bus Information. The Pyrgos main bus terminal has just created their website.
It is Google translated so you should be able to get the information you need.