The best thing you can do that will cost you absolutely nothing, zero, not a penny,
free, is to read all the possible threads on this website that have anything to do with mining BTC (or alt coins), hardware, speculation, mining support, tech support, pools, etc., and
READ and understand what is and isn't possible and the best options for someone in your situation. Find a
few good mining calculators and see how the costs will add up and what your potential profit will be under different circumstances.
There is no hurry to spend any money. There is only knowledge. That knowledge is priceless. Once you understand EXACTLY what you need to do to start off slowly and cheaply, then and only then should you spend any money and take it slowly. It may seem like you're missing out all the money that can be made but doing it right the first time will be well worth it.
When you can explain BTC mining to a stranger so that they understand how it works and the costs, pro's, con's, etc., of mining, then you are ready.
That may sound extreme or ridiculous, and a waste of time while you aren't making any money, but it is for the best.
$100 +/- is not going to get you to any level where you will make any kind of $. You may very well want to read all about alt coin mining too depending on your total budget. That may well be the best way to start and work your way up.
In reality, unless you have a few thousand dollars to put out, you may spend a whole lot more money than you will ever make.
Start with what you have and see what that will get you as far as possibly mining alt-coins (if necessary) with the hardware you have or by adding fairly inexpensive GPU's. You should know off the top of your head what your power bill will be at certain levels of hash rate. Know about what fluctuations in coin price, difficulty increases, the cooling costs, the outdoor/indoor temperature. All of that
BORING stuff.
You won't regret it in the long run. It may seem like you're wasting time and not making any money. But the knowledge and insight you will gain will be priceless in the end.
Participate in the discussions on this website and read as much as you can stand and ask questiuons. Not just broad, "in general questions" but specific questions that will take you one step farther along the path to being a serious miner with the goal of making money. Because if that is not your goal, then you are just a hobby miner and that will be a hobby that can become expensive.
Best of luck to you and I hope to see you posting on different threads of Bitcointalk
answering and asking questions in different threads. At that point you will be glad you took it slowly and you can look at your bank account and smile - because you will be doing something many, many people try to do but fail - make money mining.
GOOD LUCK!!
