If you cannot invest, you can join bounty campaigns for free. You can earn Bitcoin by participating in a signature campaign like what you have right now. Tokens that you are going to receive in your campaigns can be used as your starting money if you want to buy other coins.
I agree with you, you don't need large amount of money before you start to work in Bitcoin; there are numerous campaigns that can give you profit. Thus, you need to do research so you have an idea about the forum.