In short
Varanasi is the holiest place in Hinduism: dying here and being cremated on the ghats of the Ganges releases you from the cycle of rebirth. Thousands of pilgrims come for that.
Eighty ghats line the river over six kilometres. Manikarnika and Harishchandra are the cremation ghats, where the pyres burn continuously.
What it really costs
This is one of the cheapest cities in India. Guesthouses in the lanes near the ghats cost a few euros a night.
The dawn boat, to watch the sun rise over the ghats from the river, is negotiated by the hour and stays modest.
What nobody tells you
Cremations are not photographed. It is a strict prohibition, enforced by the families present, and breaking it means immediate confrontation.
"Guides" offer to take you to the cremation ghats and then ask for a donation towards wood for the poor. It is a known and organised scam.
The Ganges is heavily polluted at Varanasi. You do not swim in it, whatever local practice you see around you.
The city is demanding: crowds, noise, narrow lanes, the constant presence of death. Many travellers cut their stay short, and that is an ordinary reaction.