Talk to your teacher about any problems you are having with the subject matter. Make an appointment for a time before class, during lunch or after school to discuss how you may be able to get extra help. The teacher may be able to explain the problem to you one-on-one, which could clear up the difficulty.
Get together with classmates to exchange ideas and see if they may be able to help. Often what one child doesn't understand, another will, and they can easily explain things. A group study session can be a cheap alternative to paying a tutor, and a student can learn while socializing with classmates.
Check with your school's administration office and see if they offer tutoring times or services. Many schools will utilize students who are advanced in certain courses, like math or science, to tutor for free those who are struggling.
Look in your local phone directory for tutoring services in your area. Many places offer tutoring for a variety of math courses, so call around to find the highest rated and most affordable. Or ask other parents or friends for recommendations.