They are expensive. No real way around that especially if you look for brand names (if you can even find any brand names to begin with).
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2.4GHz 1 Mile (100mW) seems to be around $500-$600 for the transmitter, receiver, and camera, so that Ebay auction is looking like a steal. People use this kind of thing (the Chinese bulk kind) in their RC planes. Is that enough trust? I don't know what happens to your bot if you lose video, but it can't be worse than a pilot losing his video. There aren't any real alternatives to these "Chinese" things either because everything else is far too expensive (if you can even find it to begin with).