This is just an example to show that you can get an i5 and a 280x for that price. I don't necessary advise you to get all these parts, you have some different products and retailers than we do (AUS).
PCPartPicker part list / Price breakdown by merchant
| Type | Item | Price |
|---|---|---|
| CPU | Intel Core i5-4460 3.2GHz Quad-Core Processor | $177.99 @ SuperBiiz |
| Motherboard | Gigabyte GA-H81M-HD2 Micro ATX LGA1150 Motherboard | $35.98 @ Newegg |
| Memory | Pareema 8GB (1 x 8GB) DDR3-1600 Memory | $47.99 @ Newegg |
| Storage | Western Digital RE3 1TB 3.5" 7200RPM Internal Hard Drive | $44.00 @ Amazon |
| Video Card | Sapphire Radeon R9 280X 3GB Video Card | $199.99 @ Newegg |
| Case | Thermaltake VL80001W2Z ATX Mid Tower Case | $22.99 @ Micro Center |
| Power Supply | EVGA 500W 80+ Bronze Certified ATX Power Supply | $34.99 @ Newegg |
| Operating System | Microsoft Windows 8.1 (OEM) (64-bit) | $87.88 @ NCIX US |
| Prices include shipping, taxes, rebates, and discounts | ||
| Total (before mail-in rebates) | $716.81 | |
| Mail-in rebates | -$65.00 | |
| Total | $651.81 | |
| Generated by PCPartPicker 2015-05-12 08:50 EDT-0400 |
You may be able to squeeze in a 290, or you may just wish to get an SSD or get a better PSU or case etc.