The dynamic duo at the Design Mechanism have produced a 'basic' version of RuneQuest 6 and made the PDF available for free (though donations are appreciated). It is available at DM's website (download page) or at DrivethruRPG.
Here is Loz's announcement from the RPGsite:
We are releasing RQ6 in a much-reduced, introductory PDF edition called RuneQuest Essentials. Designed for those who want to try RuneQuest before migrating to the full rules, it offers a great way of getting to know one of the most celebrated roleplaying game systems out there.
What's more, RuneQuest Essentials is free. You can download it from www.thedesignmechanism.com/downloads (or via DrivethruRPG and our publisher page there). If you feel we're being overly generous, then there's a Donate button you can use to make a contribution of whatever you feel appropriate - or, at Drivethru, you can Pay What You Want.
What we want is for you to try RuneQuest. We'll be publishing an introductory scenario, Sariniya's Curse, very soon, and there's already a wealth of additional free material available on the Downloads page.
So if you've never tried RuneQuest before, there's no better time, and no better way, than with RuneQuest Essentials.
As I've mentioned before here, RuneQuest 6 is the best FRPG to have been published in the past two decades. Check it out!