As best we know, the sat Kartar you describe is not a coin, but a Temple Token minted in copper or similar metal. It is associated with the now-worldwide Sikh religion which originated in the northern Punjab province of India.
The token in our picture comes from respected eBay seller Treasure-India and CoinQuest thanks Treasure India for use of their coin photo.
Typical retail prices range from about 400 to 1500 INR (India Rupees, about $8 to $32 US dollars) and, as always, tokens in high-quality condition command higher prices.
The main problem with items like this is authenticity. There are modern pieces produced with the old 1804 date. These modern pieces are worth a few dollars; genuine pieces are worth more. Be sure any token you buy is genuine.
Treasure-India provides an explanation of this token in its Sikh context:
'The token depicts the founder of the Sikh faith, Guru Nanak (AD 1469-1539). Guru Nanak taught his followers to have faith in the one true God and encouraged them to worship and recite the name of God.
'On the obverse of the token he is shown seated under a tree between two of his companions. Bhai Mardana, a Muslim, is seated on the left playing a rebab (stringed musical instrument) whilst Bhai Bala, a Hindu, is on the right holding a chowri (fly-whisk). The principle of equality of men, promoted by Guru Nanak throughout his life, is represented by showing members of the different faiths sitting together.
'On the reverse its shows Guruji sitting alone.On top is written SAT KARTAR meaning Only the name of the Lord (Kartar) is True.'