Brokers like FxPro will allow you trade 0.01 lot size of gold with as little as $10 on a 1:1000 leverage account. But, remember that opening a gold trade is not the problem, keeping it open is the real headache. Even on a 0.01 lot size of gold, every pip movement is worth up to $1 so if the market moves against you, the $10 will be blown up quickly.