The mind wanders when it is not being used...
Just saw this
http://cgi.ebay.co.uk/2000-DUCATI-60...QQcmdZViewItem and wondered how much it cost to run per mile. Finger in the air guess would be close to £10, covering depreciation (original purchase price less resale price), a couple of services, insurance (although probably on a multi-bike policy) and petrol.
I reckon the KTM that I sold a couple of months back cost me in the region of £1 a mile and I think that is higher than it should be because I only had it for a year and the depreciation would be lower in the second year.
I don't have a definitive for the 900 FE because I haven't sold it but going off the price that one sold for very recently it's about 15p.
I don't even want to think about the 900SS because of how much has/will be spent on it - however much it will get ridden eventually it will still be a big number.
So what's your number?