I need to calculate the spend within each month from a start and end date that crosses a month - is there a formula that can do this?

So inputs are
spend= £10,000
start date: 30/10/2012
end date: 03/11/2012

Output I need
spend in Oct: £4,000 [obtained from £10,000/5 (total number of days)*2 (number of days in Oct)]
spend in Nov: £6,000 [obtained from £10,000/5 (total number of days)*3 (number of days in Nov)]

Thanks
Anna