Hi and welcome to FlyerTalk.
Where do you live and what sort of flying do you usually do? I presume you are aware they do not have a cash value.
I recently purchased a Premium Economy ticket LHR-ICN-LHR for £895 and upgraded to Club World with 30,000 Avios. The cheapest Club World fare was over £2000, and even using a trick like starting from Amsterdam it was £1500, plus the hassle of doubling back through Amsterdam.
So it could be said that for 30,000 Avios I got £600 of value, but this value is very personal and depends on your flying patterns, routes and desire for premium cabins.