It depending your want to start, now forex online trading can start with low deposit even use $1 trader can use the micro account, but the trading condition in the micro account is different with STP and ECN account, and to start trading in STP or ECN account, start with $200 already good initial capital, but they also need to measure trading skill, if not yet ready they can invest small money to start.
In addition to your experience, your strategy also depends on how much you invest in trading. You must have a good understanding of price action and indicators. The more you invest, the more you make. Your strategies and experience will totally determine your profit and loss.
It doesn't matter how much money will you invest in trading actually. The matter is how will you turn your initial deposit into millions. If we speak about intraday trading, then it really doesn't matter because everything will be depend on your skills, knowledge and the main goal for you is not to lose money, but multiply them. If we will talk about investing, then here, sums of money matter, because the more money you will invest the more income you will get. Investors, generally, are aimed at long-term investments and they invest lots of money in order to get income in future and have an opportunity to extract their money.
Start with money that's really small. There are cent accounts nowadays so your 50 bucks can act like 5000 on a cent account. It will allow you to experience a big account without much risk. When you can consistently make money month after month for let's say 6 months, then you can move to a standard account with a bigger capital.