Forex trading could be expensive. Sure, it may not take much money to open that account, but it is very easy to get caught up in it and put more money into that account with the possibility of earning so much more.
It is very easy to rationalize this to yourself, especially since it is so easy to move money around these days.
You need to sit down and give your household budget a long, hard look before you get into this kind of trading to make sure that you are not investing more than you can safely afford to lose.
Again, this is another time to be brutally honest with yourself; the mortgage company won't take too kindly to your situation if they don't get paid.
Consider your practice trading account
If you have joined one of those forex trading sites that offer an online practice account then you would do well to actually use that practice account.
If you use it regularly and carefully analyze your practice trading results, then you can have a reasonable idea of how much you can afford to invest with. Use your practice forex trading account as the tool that it is intended to be.
While it is great to play around, you should take it seriously so that when you are ready to invest with your own real currency, you will be better prepared to trade and can, to some extent, predict how much money you are at risk of losing.
The question of how much money you should invest in forex trading is one that cannot be answered by anyone but you.
Based on your own forex trading abilities and your own judgment in regards to trading, plus your performance on your forex trading site's trial member account, you can decide how much to invest.