Also, look on eBay for some good deal on them. I got mine for just over $100.
I will state one thing before someone else meantions it. There is one alleged downside to using these things - the motors supposedly break down easily. Don't know if that pertains to the Light Rail 3.5 in particular or if automated light movers in general, but this is what some people have meantioned. Personally, I've been using mine over 6 months now and have had no problems. It probably is related to how moist/humid the setting is that you are operating it in. I don't have a large tank and my canopy is rather open-air with fans blowing air out of it. This might have something to do with my continued success with them; don't know for sure.
Another thing that should be meantioned is that you'll need a rather high canopy for these units (certainly higher than average).
Aside from these problems, they are soooo worth it. They are a far more efficient means of using light and they allow for light to reach places that it normally wouldn't. Myriad of other benefits. Even if my motor went out on a continual basis, I probably would keep on buying replacements.