I would say that you would have to order a min of 4 55W PC bulbs to make it worth the effort, and really is it??? You can go to your local lower mainland aquariums stores, spend $180.00 with tax and have your 4 55W PC's in hand, no risk of shipping damage, easy ,easy ,easy. If you order 4 55W PC's from Pet Supply Liquidators, it will cost you around $150.00 with tax, shipping, and duty, it could be more though. Shipping in the USA is great, once it gets to the border its hell! If you want to save $20-$30 buying 4 lights you can, but I think it would be wiser to support your local stores so they can continue to bring in nice livestock for you to oggle over...
But hey if your a finatic and need to order 16+ bulbs to replace the bulbs in you 4+ reef tanks, I understand, its just too tempting with huge savings. In my opinion, it isnt worth it unless you are buying 8 or more bulbs at a time...