A relay loom is just a simple 4 pin relay, an inline fuse holder, plenty of terminals that fit over the relay pins (bulbs have the same dimension pins so you'll need 4 there as well, plus you're likely to drop a few and never find them again
) ), and a length of wire. You can buy these yourself from anywhere you wish, and add the relay to any hid-kit, cheap or expensive. I have the best cheap HID-s but without a relay kit and i suspect one of them has burnt out my headlight adjuster motor on one of the headlamps. (quite a common bug of hids this).
So buy the best kit you can find + a relay (30A) and fuse holder (with a 15A fuse) and some reasonably thick gauge wire (hids draw a lot at startup, so make sure the wire can carry at least 15A as well). Use one of the headlamp plugs that power the dipped beam to command the relay, power the relay straight from the battery with +12 (Place the inline fuse close to the battery end of the wire) and from the other pin of the relay you power up the hid ballasts. Ground them to the chassis.
And that's it, the rest is just connecting the hid bulbs to the ballasts, and tucking everything away, mounting it securely, vibration free (I use some of the foam in the hid box to dampen vibration), place them away from splash zones, and you're good to go. Check headlight aim, preferably aim them a bit lower and more to the side of the road not to upset the drivers coming the other way