Police say they hope Buckingham Palace will contribute to costs caused by the change in the royal wedding date.
Police said the men had not breached the castle's secure area
The switch in date may result in a big rise in security costs as extra police are drafted in on their days off.
A security headache occurred when two men entered a private area of Windsor Castle, although Scotland Yard said the castle's secure area was not breached.
And Prince Charles is preparing for his last official UK engagement as a single man, ahead of his wedding to Camilla.
Prince Charles and Mrs Parker Bowles will marry at 1230 BST on Saturday at Windsor Guildhall before a dedication service inside the castle.
This will be followed by a reception, which the couple intend to leave at around 1800 BST.
Hundreds of officers from the Thames Valley and Metropolitan forces will be deployed to police the wedding, which was postponed so the prince could attend the Pope's funeral on Friday.
Sally Hannon, chair of Thames Valley Police Authority, said the date change would be costly and she hoped Buckingham Palace would make some contribution.
"What we don't know yet are the additional costs of changing the date of the wedding and I'm sure that when the authority meets later this month it will ask for some support," she said.
"We probably will ask the palace for a contribution because, though we don't know the actual amount yet, it is likely to be large."
A Clarence House spokeswoman said the security arrangements were a "matter for the police and the Home Office".
She said police had been contacted by the royal household about the date change and that most of the costs involved public areas outside the palace.
A Home Office spokeswoman said the additional funding costs incurred as a result of the change in date have been "discussed and clarified" with the Metropolitan Police commissioner.
"If they feel it appropriate, they are able to apply directly to the home secretary for additional funding for a special event," she said.
Meanwhile, Windsor Castle staff are investigating how two men entered one of its private areas, days before the wedding.
Scotland Yard said the tourists were detected immediately and taken back to the public area but not arrested.
"The secure area of the castle was not breached at any stage" during the incident on Sunday, a spokeswoman said.
The Prince of Wales is set to visit a breast cancer charity in London as his last official UK engagement before his wedding.
The prince is a patron of Breast Cancer Haven and will visit the charity's centre in Fulham on Thursday.
The new wedding date has also affected the Grand National at Aintree, with a change in start time from 1545 BST to 1610 BST.
More people will watch televised coverage of the big race than the royal wedding, according to a poll carried out by ICM for bookmakers Ladbrokes.
It found 18 million people intend to tune into the big horse race, while nine million are set to watch the historic blessing at Windsor Castle.
Weathermen say it is set to rain on Saturday, with Windsor having quite chilly temperatures of 6C (43F), which is lower than the seasonal average of 12C (54F).
In keeping with tradition, Prince Charles is being kept in the dark about his bride's outfit.
Camilla has reportedly had six outfit fittings and 10 hat fittings and will take part in a final dress rehearsal with her design team on Friday.
Three other weddings booked for the Guildhall on Saturday will not be disrupted.