If you plan your undergraduate education carefully, take the right courses, get good grades, do well on the LSAT, and get accepted to a law school, the next hurdle is figuring out how to pay for law school. Tuition (full-time) can range from as little as $13,000 a year to over $70,000 a year, with many law schools somewhere between $40,000 - $50,000 a year, not including living expenses which will add thousands more annually. This does not mean that you should only apply to the least expensive schools or that you have to give up your goal, but it will be important to think about financing your law school education even before you know which law school you will attend.
If you are considering public institutions, be sure to consider not just in-state vs. out-of-state tuition but whether you can gain residency while attending school. In some states if you are independent (not a dependent of your parents) you may only have to pay out-of-state tuition for one year before qualifying for in-state tuition, while other states may require you to live and work fulltime before qualifying for in-state benefits.
Most of the approximately 200 ABA-accredited law schools require the use of the Free Application for Federal Student Aid (FAFSA). Note that if your income is verified by the previous year's W-2 form, you will need to wait until you receive your W-2 form to complete the forms. The U.S. Department of Education's Office of Federal Student Aid collects and analyzes the financial information you provide in the FAFSA and sends that information to financial aid officers at the law schools you designate, who then determine what sort of financial aid package to offer. Requests for financial aid do not affect prospects for admission.
Do not avoid applying to a particular law school just because the tuition is high, but do not ignore the cost either. With careful planning, you can arrange a financial aid package of grants and loans to combine with personal savings and part-time earnings to pay for your schooling and living expenses, however be sure to consider the amount of debt you will incur during law school and your career prospects and potential salary that might follow. As the saying goes, "If you live like a lawyer while you're in law school, you'll live like a law student when you're a lawyer."