Re: Lets calculate
It's worth looking at various sport associations in your country for funding, such as the ministry that handles sport (almost every government has one) and private scholarship opportunities, often funded by wealthy people for charitable reasons. They don't necessarily have to be specific to tennis, just sport in general. If that fails, then you would need to find a private sponsorship, where you would be obligated to pay the money back, often with interest. If you find a sponsor, most likely you can then find a commercial brand to provide you with stuff like shoes and rackets. They won't pay you money, as in an endorsement deal, but you'll get your equipment at a discount or for free.
The road to playing professional tennis is pretty damn expensive. There are so many elements that need to be financed, aside from the obvious rackets, coaching, etc. Health insurance for example, which is extremely costly. I remember reading that Marat Safin secured a private $300,000 sponsorship, much like Ana Ivanovic, and that's why he was able to train in Spain. Now, that may seem like a lot of money, but he lived on a tiny budget until he found success. I think that goes to show how expensive it is to become a tennis pro.