If you do a Google search for "vital records" from any state in the United States, you will get a long list of websites offering copies of birth, death and marriage records for a fee. It is sometimes difficult to filter out the "for profit" commercial companies that offer to provide these records from the official government agencies. If you are not careful, you could end up paying much more than the official cost of these records.
In addition, as genealogists, we seldom need the "certified" copy of these records. Certification of the record simply means that the agency, usually a department of public health, puts a stamp or seal on the record certifying that the record is an "official" copy of the original. This service may be necessary for job applications or for passports, but it is not usually a requirement for simply obtaining the information. If you are directly involved in the death of a friend or family member, you probably had to obtain a number of official certified copies of the death certificate to provide to insurance companies and other organizations. A scan or photo copy of these official certificates will suffice for genealogical record keeping purposes.
I have seen a huge difference in the cost of copies of vital records across the United States. For example, Arizona has a free website that has digital copies of birth and death certificates. The birth certificate collection covers the years from 1855 to 1939. The years for death certificates go from 1870 to 1964. See Genealogy.az.gov. Of course, if you want to, you can also pay for exactly the same certificates.
California charges $25 for a birth certificate and $21 for a death certificate. See California Vital Record Fees. On the other end of the spectrum, Florida only uses a commercial company for copies of its vital records, unless you want to apply in person or by mail. Additionally, the state office does not accept credit cards. Florida death certificates are $15 and birth certificates are $19.
To avoid paying extra and possibly unnecessary fees, be sure to start your search with the official state agency that maintains the records