"Right now we're looking at around $3,500," public works spokeswoman Gloria Chan said.
Feathers, trash and debris from the annual pillow fight in 2010 cost the department $35,000 to dispose of, according to official estimates.
Bad weather likely led this year to fewer attendees, which contributed to the lower cost.
Chan said that between 300 and 600 people attended the event this year.
The pillow fight is not an organized event, Chan said. Organizers do not apply for permits that would provide portable toilets and security and cover the cleanup costs.
"It diverts our resources and manpower," she said.