You may want to do a little more self-searching: why do you want to become a professional mathematician? Do you really want to be paid for doing mathematics? Or is it that you want to do mathematics and also want to pay the bills?
There are many costs to doing mathematics professionally. In my case I saw the potential for a high cost involving interoffice or departmental politics that I wanted to avoid, so I chose not to pursue an academic career. The other costs you can imagine or inquire about separately. You can probably infer what the costs are for doing mathematics in an industrial situation, such as the pressure to produce results at a business pace.
If you decide that you do want to find an industrial niche in which to do mathematics, I recommend talking to the employees and employers to find out what it takes to get there. Some employers may have a great enough need that they will fund your way through school.
I have other suggestions, but they should wait until you have a specific and well-thought-out goal. (You might have that already, but I do not glean that from your post.)
Gerhard. "Ask Me About Amateur Mathematics" Paseman, 2012.02.11