I second used if you can find a good junkyard. Since it's not uncommon for a hub to last a couple of hundred thousand miles, a good used one could last the life of the vehicle. Make sure you get the correct ones. Earlier XJ's with cast rotors take a different hub from later ones with composite rotors, and later ones yet went back to cast. I think your 94 should have composite. You can confirm by looking at the outer edge of the rotor face that the wheel seats on ( I think of it as the top of the hat). Composites are slightly rounded, cast have a sharp edge.
You might be able, as xjnation suggests, to do it in a half hour with ordinary hand tools, but if the hubs are rusted on, it can be a real pain, and you'll also need a pretty big wrench to get the 36 mm. axle nuts off, so having a mechanic friend with a lift and experience is a very good thing.