To physically install the hard top, assuming you have a 2 door, you should have 6 torx bolts (or aftermarket 'quick bolts'), 6 special retainer nut/clips that sit in the rear tub of the jeep, and the 2 large screws that hold down the freedom panels, and of course the hard top itself.
If you want to have the rear defrost, rear wiper, and rear washer work, it gets a bit more involved. There's line that runs to the back for the washer that I wouldn't expect to exist if the jeep originally came with only a soft top, and a wiring harness that I believe also isn't there.
These can be added, though your wipe controls probably won't have the additional control for the rear wiper, and if you don't have heated mirrors, I don't think there's any switch to tell the rear defrost to come on. Quadratec has a kit
, the instructions for it should give you an idea of how involved it is.
Of course, if you don't care about the defrost or wiper, it may be less of an issue.
As for aftermarket hard tops, all the ones I'v seen cost in the neighborhood of $2000. Used, of course, who knows, someone will probably chime in and say they got a hard top for $200 off craigslist...
Personally, I decided it sounded easier to get a jeep with a factory hard top, with all the wiring and everything else ready, and then add a soft top, than to do the other way around.