from the ports of Triest, bari, Brindisi, the ferry goes. I don´t know the prices as it has been a few years since I travelled that way. Depending on where in Greece you want to go to you can go to Igouminitsa or further south to Patra. Travelling on the ferry has beome more expensive, although if the weather is good you can even just book a seat or deck place, instead of a cabin. It also depends what ferry you get(how lucky you are) as we once had a really great one that even had a pool.From Bari to igoumenitsa it takes between 10 to 12 hours (try overnight)
hope you have a good trip Greece is great!