This will be an interesting exercise, although TiHabanero may have me beat with that nice original purchase price.
As you can see to the right, I ride a 1992 Specialized Stumpjumper FS. I used to have a road bike, but I traded it for a bike stand a long time ago.
Original purchase price, ~$800. I swapped out the stem, seatpost and its QR (~$50?). Did a sex-week bike tour on road and dirt, so I added a rear rack ($40?) that I still use, and panniers $(~$80).
All told, I doubt I have spent more than $2000 on the thing over the years between tuneups, tires, chains and general maintenance, etc., and have probably ridden close to 20000 miles on it since 1992. So, I'm gonna say around $0.10/mile.
And now I get a $50 bonus for commuting every month, so that offsets it even more!