In most cases, local governments use direct cremation to dispose of unclaimed bodies and the cremains are stored for a set period of time. After being stored the cremains may be scattered. The Cremation Society of North America has estimated that there are currently 2 million unclaimed cremated remains in the U.S.

Some counties elect to bury unclaimed bodies. Typically, the body is buried in an unmarked grave that is county-owned. If a family member later comes forward the body may be exhumed upon request.

Other states allow for unclaimed bodies to be donated for medical science. There are also state laws that allow for the unclaimed bodies of veterans to be buried by third party groups.

Source: Direct Cremation

This is for unclaimed bodies, if your body is claimed by your family then the cost is taken out of your estate or your family have to pay for it.