Okay, so you have a healthy dose of curiosity, and there are about a million things you are itching to learn. Unfortunately you are also on a budget, and let’s face it, learning can get expensive. Welcome to the real world.
The good news is that the internet makes it relatively easy for you to learn almost anything for free (or at a steep discount). The bad news? Well, there are a couple of those. The first one is that, when it comes to professional qualifications, some sort of paper trail is usually required. The second one has to do with the fact that there are some subjects that are better suited to this approach than others. The third one has to do with the fact that while independent research can carry you a very long way, it often takes a lot longer, and even though we tend to forget this because we are no actually being formally charged for its use, your time is a limited resource that you want to allocate as efficiently as you can. In that regard a book, or an organized course, can present the information you are looking for in a coherent fashion, though the trade off is that your perspective may also be artificially limited by the author’s choices.
As you can see this is not necessarily a straightforward choice, and there are significant pros and cons both ways, but before we go any further, let’s tackle the financial aspect of things.
I am not too fond of reducing learning to a matter of dollars and cents, as I don’t think this should be about money, but one way of looking at it would be to try to guesstimate how many hours would it take you to track down the information you actually need, and how much effort are you going to have to pour into sifting through things that are either superfluous, or only serve to muddle things in your mind, often with a limited understanding of the material in question, as opposed to just biting the bullet, buying and a book on the subject (or an app, or signing up for a course, or whatever). If the money you would earn if you were to spend those hours at work is more than what you would make in that same amount of time, consider it money well spent; if it is less then chances are you are better off going the free route. Of course, this is not necessarily and either/or kind of situation because there are some additional options out there
You may also want to keep in mind the fact that not all learning materials are created equal, and that the fact that something is expensive doesn’t necessarily mean it’s good.
Granted, books and professionally produced/marketed materials usually have a level of quality control that is higher than that of less established sources, such as personal websites, but there are some awesome resources out there that are both free and well organized. There is wikipedia, and the personal and institutional pages of a number of professionals who are truly passionate about their subjects, and who are more than willing to share. In addition to that there are also a number of sites that can be said to follow a sort of middle path, such as edx.org and coursera.org. These provide courses that are both organized and backed by established learning institutions that are usually free, though you do have to pay if you want to get a certificate, which can be used out in the real world, thus overcoming the problems caused by that lack of a paper trail I mentioned above. In fact they even provide some courses that can count as college credits.
Over all I do think sites like edx and coursera offer the best of both worlds, so they make for a logical first stop. The problem is that there are plenty of subjects that are more practical and less academic where those sites are simply not an option.