You're not going to get something made of aluminium for that price. Cheapest CNC router I've seen recently are the 6040 ones sold on eBay. These will set you back about $A1700 including shipping.
Working area for these is 400mm x 580mm so a fair bit smaller than you require.
For your budget, MDF construction is your best hope. Browse a bit more here to get a better idea of what's possible on a limited budget.