As others have said, freelancer incomes vary greatly.
I've been earning a comfortable full-time living as a freelancer for the past six years, although it's a mix of writing books, articles, paid blogging, public speaking, some paid broadcast gigs, etc. I'm one of those nonfiction hacks who is more in the "brand business" than the "writing business," if you will, having become an "expert" of sorts in one particular niche.
While that model doesn't make sense for every freelancer (or even very many), the thing I'd stress is diversifying your income streams as much and as quickly as possible, even if it just means targeting the broadest possible range of print clients. Eggs in a basket thing, you know?
If you can anchor your portfolio of clients with a regular gig or two, that can make a huge difference in terms of the practicality of making it work full-time. The bit of advice I would offer there is to pitch clients on letting you blog for them on an ongoing basis; much easier to land than a print column anymore, and also becoming quite lucrative compared to print. It also allows you to build your platform while being paid to do it.
Good luck.