Adding power steering and disc brakes makes all the difference in the world. Cost and labor is all dependant on how much work you do yourself and what your parts source is. I know that I can convert to power steering for under $150 with a steering pump, box, and bracketry from a junkyard. I also know what to look for in the junkyard which helps. Belts and hoses are going to be standard Jeep parts new from the parts store. I can do disc brakes for less than $200. Again, I know what parts fit and which don't, where to get them, and how it all goes together. I do use new parts for the calipers, pads, etc. Stainless Steel Brakes Corp. sells the same "disc brake conversion" in a kit form that I can piece together for about $1100 last time I looked.
If you're seriously thinking about doing either of these yourself go to Yahoo.com or Google.com and search on "Jeep Power Steering Swap" and "Jeep Disc Brake Swap". You'll find lots of info and recipes for doing it yourself. Asking about it on forums like this will get you lots of conflicting info, much of it from people who have only read about it.
The biggest thing I can recommend for doing it yourself is lots of research. Many different makes of vehicles have parts which will work on your Jeep. For example AMC Eagles used the 258 engine and they are great donors for power steering pumps and brackets if you have a 258 in your CJ. They are plentiful in junkyards. Wagoneers (also lots in junkyards) are good donors for the steering box and pumps/brackets if you have a V8. My disc brakes use Chevy truck calipers and caliper brackets with Jeep rotors. If you limit yourself to just CJ's as parts donors expect to pay much more than if you research what other parts would work.