I've seen many people here say that it is possible if you have a certain skill especially programming/web design.
Alright, let's put this in a programmer's perspective:
I am a programmer. I make websites and stuff. I may have a full-time work. Or maybe part-time. Or maybe I am a freelancer.
I may have 5 years of experience or maybe no experience in the real world. Eventually I learned about bitcoin. Now I want to use my skills to earn. The question is, how can I make my prospect clients believe that I am an experienced developer?
Even making a portfolio would cost me around $5 do get a domain for one year, web hosting not included.
So the answer is no. You have to at least invest something in order to earn something. That's a real life advice for ya.
- drwtsn32 (3yrs Web Developer, Freelancer)
On the flipside, it is possible to make $100 even in a day if you are lucky with gambling. But you also need to have a base money.
One way or another, you need money to start with.
But getting a domain can usually cost only a dollar, hosting is pretty much free with heroku, bluemix and the likes of which I pretty much host most of my portfolio sites, its a given that they would not be suitable for large sites but for personal projects and for clients to view only they are more than enough. Pretty much every awesome service has a free option.
OP can pretty much make 100$ in a month on the side doing nothing but simply finding bargains at thrift shops and reselling them on ebay.
When there is a will there is a way.
Although I have to agree that to get something, something must be invested in return.