Any site that advertises "cheap Vicodin" is very unlikely to be a legitimate pharmacy. Vicodin® (hydrocodone/APAP) is a narcotic and is classified as a controlled substance in the United States. As such, it is subject to regulation by the Drug Enforcement Administration (DEA). Because Vicodin is a controlled substance, there are strict rules for obtaining it, and there are strict fines and penalties for using or trying to buy it without a prescription.
It is not safe to try to find Vicodin cheaply or to obtain this medication without a prescription. Because you can be assured that you are getting the "real thing" (not a counterfeit or expired medication) only from a legitimate pharmacy, buying Vicodin (cheap or not) without a prescription increases your risk of getting a substandard or dangerous product. Some Web sites offer to provide a prescription for Vicodin after a "consultation," usually consisting of a short questionnaire. This is not considered a legitimate prescription, and no legitimate pharmacy would fill such prescriptions.
Also, without a prescription, legitimate Mexican pharmacies will not sell you Vicodin. It is not any more legal (or safe) to buy it without a prescription in Mexico than it is in the United States.
(Click Buy Vicodin Without a Prescription for a more in-depth look at this topic, as well as information on the steps to take to find a legitimate pharmacy.)