The official language is Irish Gaelic and spoken in most areas as the first language. English is the other official language spoken.
Greenwich Mean Time
In Ireland it'll cost you about €5 (approx $8) for a pint of beer... get that Guinness down you! It's the native land, after all.
If you're looking for a cheap meal in a pub, you're expected to pay between €8-€15 (approx $12-$24), or if you're feelish flush go for a 3-course meal, which is around €70 (approx $112).
Catching a taxi on a basic tariff will start at €4 (approx $6.40) and add about a euro per km. In the cities, hop on the local transport for about €2.50.
A one-way ticket on public transport in the cities starts at about €2.50 (approx $4). Alternatively, just hit the road in a rented car or campervan & see some of the countryside!
A hostel bed in Ireland is the cheapest way to go, and can cost between €12-€20 (approx $19-$32) per night.
If you're looking for a little more than a dorm room, a double room in a hotel or B&B can cost between €80-€180 (approx $128-$288) depending on where you're staying.
In short, no. Australian's don't need a visa to enter Ireland. You'll still be subjected to immigration control though. If you're looking to do a working holiday visa in Ireland, then the entry requirements are different, and you'll have to go through a specific application process. Find out more about this on the Embassy of Ireland, Australia website.