I generally say avoid Arcadia halides, the number of prople I've had to talk though replacing ballasts, ignitors, lamp holders e.t.c on another forum is un-real. Seriously unreliable bits of kit...
AquaOne halides are up on Ebay quite a bit, actually, there is a well priced 3ft, 250W modle on there ATM, that I thought about earlier this week, before a requirement on the new tanks spec made me say, "right, another LED rig it is then"...
All the best
Rabbut