In all I invested about $500 on what is essentially now a brand new bike. The only used parts other than the frame are the wheels, but they are stock replacements and are in great condition.
Almost complete bike: $200
Hayes Mx1 Disc brakes and levers: $140
Rear cassette: $25
New chain: $10
Race Face grips: $10
IRC V-Claw tires: $20
I impressed myself by installing the disc brakes, which were surprisingly easy to do. I've heard people talk trash about the Hayes mechanicals, but even after only a few stops, they are already performing btter than any rim brakes I've ever used.
I m having a slight problem with the rear derailleur and it not wanting to shift onto the largest cog, but I hope to have that sorted out soon enough.
Took it out for a ride tonight, and it is a freaking blast! It rides nice and smooth, but it's nice and solid when I take it down some stairs or go off a small hit.
In its nice safe garage next to the wifes new bike.