Kar brings up a good point. IF you absolutely can't afford the lights now, then you have a choice:
1. Buy cheaper lights now and then possibly have to upgrade and buy the better lights anyways.
2. Don't set the tank up and wait until you have the bare minimum to have a salt water tank. (i.e. Tank, lights, filtration)
3. Set up tank with live rock and sand but don't have lights and just let the tank cycle a REALLY long time until you are ready to make a substantial light purchase.
I didn't buy what I really wanted and am now going back and repurchasing almost everything because of initial costs. If you think it is expensive now, doing it twice costs even more. Just thought I would share from my own experience.
True the cheaper lights may perform a similar job but the only way I know to see how one light performs compared to the other is to use a PAR meter and measure the two. The big difference from eBay and a reputable dealer is the customer service after the fact. If something goes wrong (everything breaks) then the reputable companies have to keep a good image and often will go above and beyond to make sure anything that is broken is fixed quickly and cost free. Drs Foster and Smith have been wonderful to me and are available almost all the time.
I do not intend to be negative or say anyone is doing anything wrong, I just hope my explaination helps convey the message about purchasing a "cheaper" product to get it now as oppossed to waiting a bit and getting better quality products.