Bicycle Tutor

Quick background. Just bought a 2006 mountain bike that was never used and stacked with decent components. Everything this is great expect the previous owner really disliked the disc brakes for some reason and completely dismantled them, leaving only the discs on the wheels. (BTW, the brakes are (Hayes 9 HFX carbon, which i think are decent)

He did give me the entire systems, calipers, wires and all that stuff, but it is completely taken apart leaving a mass of screws, washers, pads, etc.

So I have multiple questions.

1) if I buy new, different brake system, can I use the existing discs that are still attached to the wheels? (Thus not spending an additional $100)

2) Should I even bother trying to put the system back together? I have moderate mechanical skills, but by judging the manuals for the system, it looks pretty damn complicated and likely to go wrong on various front.

3) Anyone have a ball park on a fair price for installing a new system?

Thanks.

Your rotors are totally independent from everything else and not specific to any Mfr or Model.
I don't remember that Hayes model (been too many) but they make great stuff. The only little problem that I see is the advancement of levers and calipers in the last 6 years. Your call. I still prefer V-brakes because I am a weight weenie and haven't impaled myself on a broken tree limb yet.

Fair price to install? Too many variables. Mechanical or Hydraulic? Mississippi or Hawaii?

I am presuming this is hydraulic. if the hose lines have been removed from the calliper or lever you will probably need new olives to stop any leaks, also you may need to slightly shorting the lines to fit a new olive this may depend if the olive is one piece with the insert.

what exactly was taken apart Lever? calliper?

as far as I remember you need a tiny bit of o-ring grease for the o-rings.

and just glancing at the manual you need cir clip pliers for the lever if they have been taken apart.

Hayes 9 is pretty simple and there is manuals on-line with exploded diagrams that are useful.

weigh up how much it will cost to fix; olives, maybe new hose, cir clip pliers, bleed kit.

I am curious as why the brakes are in bits I know I have bought Hayes of ebay cheap because they had sticky or sized pistons. Do the brakes look used?