The government has offered to pay half the estimated cost of the police operation at the Climate Camp near Kingsnorth Power Station.
Nearly £6m was spent policing the week-long event according to Kent Police and the Home Office has confirmed it is willing to contribute £3.2m.
However, talks are continuing because the government said the force had asked for a bigger contribution.
Kent Police said the chief constable was still in "ongoing negotiations".
A Freedom of Information (FOI) request by BBC South East revealed on Tuesday that nearly £5.9m was spent on officers, accommodation, air support and planning.
'Public money'
The force said it would be some time before final bill was known.
A spokesman for the Home Office said: "We have offered Kent Police £3.2m and Kent Police have asked for more. We are considering that request."
The cost of policing the environmental protest near the Kingsnoth Power Station has been branded an outrageous waste of "public money" by Climate Camp spokesman Kevin Smith.
But Sittingbourne and Sheppey MP Derek Wyatt said the police operation was necessary.
About 1,400 officers policed the event and 1,000 activists attended the camp, according to estimates made at the time.
100 arrests
Officers made 100 arrests during the event on the Hoo peninsula, about two miles from the power station, in August.
Out of those, 46 were charged, mostly with public order offences or obstructing the police.
Twenty-two were cautioned, three were bound over to keep the peace, and one breached bail terms, the force said.
The current Kingsnorth power station is due to close in 2015 and E.On wants to replace it with two new coal units which, it claims, will be 20% cleaner.
Its proposals have already been approved by Medway Council but the government will make the final decision about the project.
Activists have vowed to return to the power plant if the decision is approved.
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