Online Marketing can be a relatively simple thing to start, however, learning to do it effectively will take some time and it will cost money. You should create a budget to spend each month. It could be any amount, but as you might imagine less money generally pays of less. If your budget is low (say $30/mo), just expect things to take longer to achieve. If you budget is higher, at first, while you are learning, you will want to find a balance between enough to be effective, but not so much you lose too much as you are working through the ins and outs.
What if you can't afford even $30/mo?
I've been there. Included in my list of marketing methods are free methods. I have found these to be useful, but I haven't achieved as much return on my time as I do with the options available when I can put some money into the methods. However, that doesn't mean they can't be successful.