Mr O'Brien said he and his wife would see that $20,000 was given to St John Katikati after the party, he said.
His Rocky Horror history had made him a bit of a face of halloween and he loved to dress up, he said.
"I'm the man who put fishnets into Halloween."
All costumes were welcome at the party and the UK expat hoped the Kiwi crowd would get into the spirit of dress-up. "People in the Bay, by-and-large, don't dress up. The men especially."
The broad theme kept all options open for people and he wanted to assure everyone "the zombie cowboy is quite acceptable".
Fundraising committee member for the new ambulance station Kate Williams said the financial boost would be a great help.
Watch: Richard O'Brien doing the 'Time Warp' here
"We're trying to get approximately $300,000 together from the community ... Richard and his wife are being amazing."
The Build in a Year campaign to raise the $800,000 launched in July after St John Katikati had met the $230,000 cost of the land and had a further $230,000 set aside for the building. The current station, built about 18 years ago, was too small now they had two ambulances and four full-time ambulance officers, supported by up to 10 volunteers.
Katikati's Halloween hoedown
*Katikati Primary School.
*Doors open 7pm.
*$30 tickets available from Katikati. Info Centre or Molly's Dress Shop in Waihi.
*Door sales may be available