Good question. I found one good ebook that works a lot for me (to make some $$$). Ebook is mine so feel free to download it here => http://pastelink.me/dl/d39387 ... (link is safe, no refs and no ads)
I would still invest $100 into bitcoins. Correct bitcoins is at $815 a coin right about now but you can buy smaller fractions of coins. I been using bitcoins for a while now and always buying more bitcoins and only selling when high to buy more bitcoins. With anyting there are risks but more and more vendors are taking bitcoins and I think this currency will not go anytime soon. https://www.facebook.com/groups/btcrobot/
When money is in short supply, turn to your other major resource, time. Invest your time in researching the issues that are right for making a blog about. Put more time into finding other people in the industry who you could submit guest content to. make a name for yourself on blogs and forums you find. When you start thinking about building a business in a low-cost, guerrilla marketing approach, I think your possibilities will open up way beyond $100 worth of potential.
I would pick a service that I could offer on freelance sites and advertise on them for free. save your $100 until you get a few jobs finished and then expand from there.
I would honestly find a bank savings account to put that money in first. So while you think, you actually have your money growing for you. Then, you might find a few investment blogs to read in addition to reading investment books. There are tons out there and a lot of them repeat the same information which should make it is for you to pick out the important ideas. Cheers.