I recently bought a rig in Aus for just over $900

CPU: AMD Sempron 140
RAM: 2GB
MB: GB GA-870A-UD3 (2xPCI-E x16 and 2xPCI-E x1)
GPU: 4 x Sapphire HD5830
PS: CORSAIR TX-850

Have this running caseless and getting roughly 1100-1200 MH/s

Hard to predict wether it will pay itself off yet, but once MTGOX
comes back up, will be interesting to see the rate BTC get.
I'm happy to wait and see how the market moves for at least
a month or two and just save my BTC.