I have a very old-school Hoodoo steel hardtail. I have about 12,000 miles on it - 2,000 miles of touring, and about 10k miles of commuting (10 years at roughly 100 miles a month, so I may be underestimating). I didn't keep receipts, but here's what I've done to it:
-new back wheel (the original wheels were nothing special; I switched to a 32-spoke wheel to address frequent cracked spokes when touring)
-New front wheel (I wore through the rim with my brakes!)
-New seat (I wore one out, I must be a hardass)
-I am on my 3rd drivetrain (chain, cassette, chainrings) because I suck at maintenance
-I think I replaced the shifters once
-Have been through a number of brake pads
-Full-coverage fenders for rain commuting
-Lights
-My Blackburn rack was moved from my last bike and must be approaching 30 years old...they are built to last!
If I had to do the math, I would guess I might have about $800 into it in parts and labor (no, I don't do my own work, facepunch please), over and above the original purchase. Getting closer to the $.05/mile point, but not there yet.