There are other things to consider when buying a HID kit. If color is your main concern, then by all means go for whatever kit that gives you the best color the lowest price. However, with cheap kits, there are things that affect the placement of the light. Cheap kits may overlook optics or they are designed poorly and do not have the bulb on the proper axis. If you want nice purple light, but your light isn't being distributed where it should...then that doesn't make much sense at all.
Buyer beware when buying HID kits. There are good, cheap kits, and their are bad, cheap kits.