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When I was researching this a brand called Cruz came up, their Airo bars use the same aero design as the previous gen aero Thule bars iirc. A full new set was the same/cheaper than 2nd hand Thule. And they are well reviewed.
That said you only need the cross bars, so have more options.
Not knocking the aero benefits of Thule/similar, but if the main use is moving a surf board then based on my limited experience of surfboards on roofs I'm not sure aero bars are going to make any difference to fuel or noise. Altho if they're not removed there is an obvious benefit.
This: the Thule roof bars I have on the A4 are silent. Even with a 9'6 on the roof. It's definitely a consideration. Maybe get the stealthy bars: http://www.rhinorack.com.au/products/roof/roof-racks/vortex/vortex-stealthbar-black-2-bar-roof-rack_ja7976
Then when you sell the car you can recover most of the cost. As you say, they are still $400 second hand.