[edited out]
you don't need to have income that exceeds your needs before investing into bitcoin. If you are waiting till you have excess income that's above your needs before investing, you might end up being unable to invest at all because needs will keep coming whether you like it or not.
By definition, you need to have either income or some side amount of savings (or other investment) that is greater than your expenses in order to be able to invest. If you do not have excess, then you are gambling rather than investing.