I kept pretty good track of two trips... a 2009 trip in the US and Canada and a 2010 trip in Europe and central Turkey. I included everything except bike prep and any gear purchased before the trip, but the numbers do include vaccinations and visas obtained pre-trip. I tried very hard to keep track of anything that was trip-specific or expenses encountered enroute.
My 2009 trip total cost was almost exactly the amount budgeted for the trip ($7,000).
The 2010 trip was under the initial budget of $20,000 but that was only because I changed plans while in Turkey and turned back through Europe instead of continuing east to Vladivostok and taking on the expensive flight from Korea. The high daily cost of the 2010 trip also reflects using more hotels (83%) than anticipated due to the absolutely crap weather for the first 6 weeks of my trip... where I did no camping at all.
Food was easy to keep on budget. If I was below budget, I splurged at a great restaurant. If I was getting above budget, I didn't eat. I just kept everything on a spreadsheet and brought it up to date every few days while enroute. That way I could see how things were going... or where they were getting seriously out of whack.
Anyway... I'm sure there are significant savings to be had. I certainly wasn't scrimping anywhere. Clearly, however, the way to keep the per kilometer cost down is to go on longer trips and ride a lot!
--------------------------
2009
British Columbia - Prudhoe Bay, Alaska - Colorado - Newfoundland - Florida - California - British Columbia
95 days
33,900 km
$7,218.25 USD = $0.21 /km = $75.98 /day
Daily costs:
Fuel = $16.10
Lodging/Camping = $23.38 (33% camping)
Food = $19.39
Souvenirs/Gifts/Entrance fees = $2.81
Maintenance = $5.43
Misc (tools, gear, clothing, other fees) = $8.87
---------------------------
2010
British Columbia - ship air to London - Scotland - Ireland - Romania - Turkey - Greece - Italy - London - ship air to British Columbia
132 days
20,300 km
$19,650.83 = $0.97 /km = $148.89 /day
Daily costs:
Air shipment of bike and self, ferries = $46.26
Fuel = $13.72
Lodging/Camping = $39.10 (17% camping)
Food = $14.62
Souvenirs/Gifts/Entrance Fees = $2.88
Maintenance =$3.06
Misc (tools, gear, insurance, phone calls, etc) = $21.48
Visas = $7.74 (didn't use Russia, Azerbaijan or Uzbekistan) 