What is a 1804 penny worth?

If you mean an American large cent, there are originals actually minted in 1804, very bad restrikes made in 1860, and fakes. A genuine 1804 cent sells for at least $2000, while the restrikes go for several hundred. Fakes are worthless of course. If you have an apparent 1804 Large Cent you should have it inspected in person by a dealer or appraiser.