96-02 Crown Vic. rear disc... we got them at Pull a Part for $45 a set. http://mmb.maverick.to/threads/stock-e-brake-system-for-rear-disc-brakes.96019/
It all depends if you are able to add them yourself, if you're paying a shop, probably more than the car is worth... The least expensive route is usually find a parts car, then take what you need and sell remainder to recoup your investment...
Yeah I was planning on doing it my self as much as possible. I don't know much but am learning as I go.
Get yourself a set of factory shop manuals, worth their weight in gold(OK maybe a slight exaggeration)... A new set was published every year but for a '73, the ones issued between '71 & '75 will have more or less same info for Maverick... A notable exception are the disc brakes, were not avail till '74 so the later ones would have the advantage...
If you have trouble with finding what you need at the wreckers a brand new front disc brake setup is $800-1200. Wouldn't bother with rear discs until you were satisfied with all the other aspects of the car. Just my 2 cents. For power steering you should be able to strip everything off a donor Maverick or Comet, rebuild the ram, and maybe just buy a rebuilt pump and new hoses. MD