What's the current conversion rate - you'll open yourself up to tons of American help if you know it, because we only know American money....or if you live in Florida, how much it is in Florida dollars

Still and all, even though I'm not positive on the exchange rate, I know most everything else required to build a cab costs more in Oz. It's why someone was considering purchasing from the U.S. and reselling over there.
Rough guestimate, I'd say Bones' figures are about correct, but completely dependent on your ability to find "reasonably priced" items....otherwise, bump it up just a touch.
Don't forget, your family and friends are the ones who will pester you the most. They'll look at it as if it's your responsibility to make it work just as an ACTUAL arcade machine would - meaning YOU are the tech support and troubleshooting and "I only have five million more questions and could you do it all for me yesterday, even though you have a job and a private life....oh, and I won't be paying you to do it and will complain about how long it's taking too".