You can start with as low as $5 capital, as most brokers nowdays offer accounts with really low minimum deposit requirements & let you trade larger positions via high leverage.
See our comparison of forex brokers in Nigeria & their deposit requirements.
But, we strongly advise against using too much leverage. And you should trade on demo account first to learn about the basics of trading. Only once you are comfortable with your strategy & it is profitable on demo, then you should consider funding a live account with low capital. If you are profitable with low capital then you can consider to increase capital for higher position size.