So I managed to purchase a fully working copy from the Steam China store, which I have tested online etc. and is working perfectly. In order to do this you will need to:
1: Download a VPN service (Hola for Chrome works fine) and set your region to Chinese.
2: Create a new Steam account, making sure you have the VPN enabled. PLEASE do not risk your existing account, as you may lose all your games and it probably won't work anyway.
3: Enter your credit-card details into your account preferences (Make sure to use a fake Chinese address and phone number. Google will help you with this).
4: Log out of the account, and search for Grand Theft Auto V, whilst still using the VPN.
5: Buy the game as you normally would (for yourself, gifting unavailable), and login/purchase when prompted.
6: Login to Steam with your new account, install and play!
This worked fine for me, and it came out at around $38 AUD. I would highly recommend it, although advise that you proceed with caution:
This technique is technically not allowed, and could result in the banning of your Steam account. Furthermore, you will likely receive no support from Steam in the case of any issues.
Enjoy your cheap GTA V!
Mod. Purchase at your own risk, from Steam: You agree that you will not use IP proxying or other methods to disguise the place of your residence, whether to circumvent geographical restrictions on game content, to purchase at pricing not applicable to your geography, or for any other purpose. If you do this, we may terminate your access to your Account.
From the Steam Subscriber Agreement
Note that it doesn't just stop you from playing GTA V if caught, you lose access to your whole account. Really not worth it.