WTB: one (1) HID ballast for 98 528i

I am looking for a single ballast for a HID xenon headlamp (suppose I would take Philips but would prefer Hella) for my 98 BMW 528i. I am buying a pair of OEM Hella HID xenon lights with only ONE ballast from another owner who upgraded his OEM xenons to Angel Eyes. I can get a new Hella ballast for $150 from www.hids4less.com, but I am interested in buying a used one for less if someone has one to sell.

Thanks for your help!

Vince
98 528i sport 5spd blk/blk