I've just had the chance to try out a sample of a new pre filter made by
Unifilter australia.

I used the filter for around 6000 km's with about 2/3rds being in very dusty outback Australia . Ride report here if you want a look :

The filter worked extremely well at saving the stock paper filter. It didn't appear to need re jetting as fuel economy was similar before and after fitting.
The filter replaces the stock snorkel by just pulling the stock part out and fitting the new units rubber base in the same hole.
It's easier to fit if you remove the airbox lid the first time but not necessary once you know how it fits.
It's a foam filter that is meant to be oiled, and is cleanable.
It didn't really need cleaning for the whole trip, just a quick tap to loosen
some caked on dirt. It should show up on there web site soon.
Not sure about the price. I'm not affiliated with the company in any way, but was lucky enough to get a sample.
A few pic's tells the story better,

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