a machine in Australia is around $4000 +
a machine for anybody is 5000/6000. you paying for the ability to make money off it.
that said, the hardware is easy to come by, it's the guns, I/O board, and the software dongle that are going to hang you up. the guns required for use with a non-crt screen (ie deluxe cabinet) are about 500 each. regular optical guns will not work on a flatscreen.
your best bet is going to be hacking up a wii and controllers, but then you just have a hacked up wii.
save your pennies and buy a buck hunter when one comes up for sale.