If I were in your shoes, I would put it all into Mediatraffic. There you can get dirt cheap pop up and pop under ads with a great targeting system. From there, I would use free hosting to make as many different types of campaigns as possible on media traffic. After getting accepted into an affiliate network of course, so you can have ads. Here with just $50 you have gotten all of the basics for learning your ropes. You have now created multiple campaigns and created multiple landing pages, helping you with your design and adwriting. You have learned how to use your affiliate network, and how to set up hosting. You have learned how clicks, conversions, ads (and the list goes on) all work, first hand. Who knows, maybe you will get lucky and make a conversion. This will likely take a complete beginner at least a month. With all your new knowledge and experience, you can think of a better strategy as to what you should do with your next $50 that you save up. All of that experience is worth way more than $50.