Yeah, the rails and hardware for your size installation (based on your support structure size) should be roughly $950-1,000 with all the hardware (including clips and T-bolts and splices) and freight to get it to you.
You can probably build something cheaper than that but the Unirac rails are designed to allow for expansion and contraction of the panels, and it's all aluminum so it will never rust or rot. When you look at what you get with a Unirac rail mounting system, you can't built it for that and make it equally as good as the "real thing".
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Chris