Only need bulbs if changing color of your headlights (D2S)...scroll down a little on the website you linked...."HID bulbs DDM" they are $30 + $5 for the pair.
If your doing the Fogs, you need a whole kit (Apexcone 35w/55w full size ballast hid kit). You will get the ballast, bulbs, and a small guage wiring kit. To wire a 55w kit, you will definately need the extra "HID accessory harness" for $25.
Remember...if going 55w, you absolutely need the HID accessory harness. This is to keep your electrical safe. And if going to 55w and want to color match, you need about 2000k difference in color. So if you want 6000k hid headlights and want the 55w kit to match..you need to get an 8000k kit for the fogs. The 55w kit washes out some color causing you to go higher in the kelvin scale to match the color from 35w headlights.
Our stock ballasts, bulbs, and wiring are all 35w. Do not put a 55w bulb in you stock headlights. Only 35w D2S..color is up to you!
Fogs Light Specs:
-03-05 = 9006 kit
-06+ = H8 kit