I'll start by saying that, in good theory, HID shoul duse LESS watts than Halogen (typically, about half for the same light level)... So if these lights use "serious wattage", then they must be SUPER bright (which I would guess they are, given the price tag).
Having said that, I used to run my YJ with the stock alternator, even though I used an eFan, 2 sets of 100W aux lights, and a kick ass stereo with Amp, and never had any electrrical issues. Since then, though, I upgraded the alternator (167A now), and decreased the wattage of the fog lights to 55W for durability of the light bulbs and because i was blinding oncoming traffic.
Now, regarding the price, what exactly do you need these lights for? What I mean is that it may be more cost efficient to look at a cheaper set of lights, as these seem to be extremely expensive (you could buy 4 sets of daylighters for the same amount, or 3 sets of cheaper HID's), and under most ussual situations, you will not be able to use them (like road driving, or even on the trail if there is anyone in front of you). Unless you do high speed desert driving, I find it hard to justify such a large investment in a set of lights...
Felipe