You'll be right, it's all about having fun and playing pinball. Doesn't matter what you score but it's fun to compete. You might surprise yourself, have a few good balls and make the finals!
You can always go to Kings over the next couple of weeks and have a practice on the three machines they have there.
Not many other venues in Melb have more than a couple of machines (that I know of) and none have pay $x for unlimited play. $5 for 3 games is standard but there are a few venues where it's $1 a play.
Check the Melbourne Pinball Finder for an up to date list.
