The U.S. Code is available in many places for free online. The official print version of the U.S. Code is published by the Office of the Law Revision Counsel of the U.S. House of Representatives, but the code is available online for free in many locations.
Free access to publications of the U.S. government, including Federal Register, Code of Federal Regulations, Congressional Record, Public and Private Laws, the official U.S. Code, and U.S. court opinions.
Don't forget to verify that the statute you are using is the current version of the law. The government issues the following disclaimer regarding the version of the U.S. Code on FDSys:
While every effort has been made to ensure that the U.S. Code on FDsys is accurate, those using it for legal research should verify their results against the printed version of the U.S. Code available through the Government Printing Office.
Another alternative is to use a citator such as Shepard's on Lexis or KeyCite on Westlaw to verify that you have the current version of the statute and that it is still good law.