Tricky one with n+1 bikes...
The Bad Boy was about £800 to start with and ate about £150 of bits a year; it's done 15000 now and is 7 years old so that's 12p a mile.
The new roadie was £400, has had about £150 spent on a wheel and tyre upgrade, but has only done 1500 miles so far - 40p a mile. Clearly I need to get out more on that one!
The fixie is pure zen as I've no idea how much it really cost to build - it took so long and got changed so much - or how many miles I've ridden it as there's no computer!
Running costs are close to nil as nothing has worn out, but I keep changing it around for sheer fun (bullhorns/deltas - moustache/offroad - pistas/trackfettle - carradice/fraudax).
(I still haven't ridden the pennyfakething but at a total project cost of £15, I ain't complaining...)