One of the easiest ways to make money online is to join an affiliate program.
Stephen has a good point. Affiliate marketing is known as the quickest method to making your first $100 online. You can do this by creating your own website, writing your own content, and then pitching your affiliate offer in your own unique way.
Stephen is also right when he says you will have competition in affiliate marketing. However this is good news because it means it is a profitable market you enter.
If you want to acquire a website that's already running, it usually would cost much much more than building one from scratch. That said, you would have to calculate the investment you make versus the cash flow the site is already making. Only you can decide whether the acquisition price is worth the return on investment you can get.