The fact that you have one indicates that it's not real, as there are only 15 known genuine specimens.
Zero
If you think it's an older replica made before 1973 and does not have "copy" on it, take it to a coin dealer.
A denomination is needed, post new question.
There were no Morgan silver dollars minted in 1804. The first year of mintage for them was 1878.
There are only a handful of genuine 1804 silver dollars known. The easiest test for a non-professional to do is just take it to a reputable coin dealer for an evaluation. Chances are, you've got a copy. Before you do this, look for a "COPY", "REPLICA", "R" or "C" stamped in the coin, if you've got one of those you have a fake without a doubt.
It's worth little to nothing. Being that it's a replica, it's not made of silver, and there's no collector value to it.
If it is a replica, not much. The only value in replica currency is the materials it is made out of, for an example a silver seated liberty quarter replica would be worth no more than its silver content, regardless of what date it said on the coin because it is a replica.
10.000.000$
Click on the link in the "RELATED LINKS" at the lower left corner of this box to see the 1804 silver dollar.
The value of 1889 Morgan silver dollar replica ranges from $23.01 to $26.76
The U.S. didn't make any half dollars dated 1804.
This is NOT an original 1804 silver dollar. The value is only worth what the metal is worth. If it's made out silver it will be worth more than if it just has a silver plating with some like a stainless steel core.