To earn bitcoin, you need investment in any case. Because you buy bitcoins to make money on their growth, or you spend money on buying and maintaining equipment for mining.
There are ways that you can earn even you don't have investment to put in bitcoin. But you need to invest somehow in internet, electricity and other utilities to market and sell out your skills to the companies. You don't have to invest directly in mining as bitcoin mining, for me isn't profitable anymore. Just be a freelancer.
I agree being a freelancer is not that hard as long as you have a skill that make your customer back to you, Just like very campaign manager here they are building trust for the new campaigns will get the m and I think that is the best and they will get the biggest profit here in the forum. That is because they build a trust and reputation here.