You could even trade if you had $5 on your account. This will depend on the leverage you choose.
For example, if your leverage was 1:500, you could buy/sell 0.01 lots of GBPUSD at 1.34861 and the trade would cost $2.70. Whereas if your leverage was 1:100, it would cost $13.48.
Each instrument has its own contract size or lower leverage, so the above statement may differ for different instruments. For instance, Indices and Commodities have lower leverage so you would need more money to open a position.