I suppose, I thought the 540 was costly enough as is, but it does what it sets out to do. The only thing I don't like is the hole in the bottom of the main enclosure, but apart from that this ticks the perfect price/quality ratio for me.
And yeah, 400 dollars is... yikes. Well past the point of diminishing returns, imo.
I have the Corsair 540 and it is relatively not that dusty. However, I think that dust is coming from the bottom of my case from the hole because dust settles at the bottom of my case.
So I have been giving this some thought;
http://www.demcifilter.com/p0431/corsair-air-540-dust-filter-kit.aspx
It is rather expensive and shipping is an extra $17. But those filters should improve airflow because there is less plastic in the actual filter unlike the stock Corsair 540 air filters.